So it would probably depend on a person's level of education and their access/proximity to literate culture, ie nobility, monastic orders, the clergy, and so on, but we have a lot of gaps to fill in and in all likelihood its probably not as exciting as you think. It also might not quite be what you're expecting!

Literate people of the time period are the ones that are best represented in surviving texts, by simple virtue of the fact that they are the ones making the texts. We might occasionally get a glimpse into what "mythologies" the people might believe in, but they will only ever be glimpses. So if you're looking to find out what Wulfric the stable hand thought about elves or dragons and so on, you're kind of out of luck for this time frame, but that doesn't mean there was no room for what we might call the supernatural or superstitious among the learned classes of people, just that everything we know comes through highly filtered sources or is conjecture based on other belief systems or projecting beliefs backwards in history. As an aside, if you're curious particularly on folklore of later England, specifically Cornwall, /u/itsallfolklore is the go to!

A few notes to start with. We cannot simply assume the practices and beliefs of the Anglo-Saxons were similar to their continental antecedents in western Europe and Scandinavia. Nor should we look to the later Icelandic sagas that dominate our understanding of "Norse mythology" as a similar culture we can supplement our scattered understanding with. There are a lot of reasons for this, but they're largely subsidiary to the overall point.

The people most likely to be literate or exposed to literary culture in England at this time are those who are in proximity to the Church. This includes, but is not limited to, monks, priests, bishops, and so on up the food chain. We know that in at least Alfred's case some level of literacy, including in Latin, was expected of royalty and probably there was some limited vernacular education among the nobility as a whole. Thankfully some of these Church, and Church adjacent, figures left some writings on these topics, though not in a direct way. For example, the venerable Bede, a monk, wrote about how the people of England were taken with using amulets to ward off illness, though as a respectable Churchman he believed that such magic was impossible and that the amulets were, at best, useless. Other monastic sources such as penitentials, books on what penance people should do for various sins (though their actual implementation is a can of worms we need not concern ourselves with here) get us glimpses at other practices that irked, or did not, Church authorities. Leaving out small offerings of grain for local spirits for example was tolerated but sacrifices of animals were right out.

Now these sources did not entirely discount the supernatural (as we would define it), and even medical texts of this time mentions the need for cures for various ailments that elves could inflict on both people and livestock. It is a rather simple leap to perhaps believe that the offerings that were tolerated by the Church were meant to placate such beings, though I do not believe that the connection has been explicitly made by a scholar. These supernatural beings/forces were first and foremost dangerous by people who believed in them and to be avoided, placated, or defended against, not sought out. There may have been other, perhaps even more extreme, examples of cynical, or theologically orthodox, Churchmen like Bede, but our base of sources is quite scattered and incomplete.

There are other examples of pre-Christian sites having some importance which held over after conversion. For some time pre-Christian sites were maintained, Robin Fleming points to some likely spots of judicial severity, ie places for executions or places to dispose of the bodies from said executions, as probably pagan sites of importance, indicating that a lingering association with these sites was maintained. We also see this in some of the physical remaining marks, the white horse of Uffington was noted on in the Middle Ages, though our sources are much later than your time frame (the horse is dated to pre-historic times in Britain, probably long before the Romans even reached the island).

Other literary sources, and quasi-relics, such as the epic Beowulf might preserve some beliefs, though texts such as Beowulf are problematic to use, as its date and place of composition, as well as intent, is still hotly debated. However it is telling that within the text of the poem the evil of Grendel and his mother is traced back through to Biblical times and to the personage of Cain. Other mythological figures are mentioned, sea monsters, a dragon (though a non-flying, ground dwelling one, and both wyrm and draca are used to refer to it but we are light on a lot of details (though it is quite long)) appears, and scholars have spilled a great deal of ink over the appearance of words that can mean giants, might mean valkyries, and perhaps hint at trolls, and so on. How seriously were these beings taken though is the real question, were they the products of a time long gone or did they still roam the Earth? The poet(s) does not really give the audience a firm answer, though given the general theme of decline and decay present in Beowulf... However, overly relying on a work like Beowulf to inform our understanding of Anglo-Saxon mythology is likely a bad idea. Other literary sources such as the "Letter of Alexander to Aristotle" take place in far off and exotic locales so their own supernatural elements cannot be transposed to the English landscape.

Tl:dr, Our sources are so incomplete and filtered we can glean very little about the superstitions and beliefs of every day people in Anglo-Saxon England. What we do know comes from literate contexts that were apprehensive about these superstitions. This apprehension could be in their effectiveness ala Bede, or in their power, ala popular charms to ward off illness or cure elf diseases.

/u/Steelcan909 has already provided an excellent answer; I just wanted to touch briefly on this part:

Folk magic was used to treat illnesses and such.

This is a fairly common assertion, and it's one we have to be quite careful around for risk of presentism, and falling victim to a kind of post-Enlightenment/Victorian teleological idea of historical primitivism that essentially dismisses historical populations as superstitious idiots. This is a real problem with dealing with "The Dark Ages" as there's a popular tendency to overlook non-Classical sources as not scientifically important.

That's not to say that magic wasn't invoked: as previously said, Bede mentions the wearing of amulets to protect against disease (although as a phenomenon this isn't radically different from the wearing of saints' tokens) and medical textbooks do indeed include charms or rituals for dealing with Elvish curses, particularly of horses and livestock. On the other hand, a lot of what today is called 'folk magic' has a genuine medical basis.

Bald's Leechbook is a 9th Century medical textbook [from the Old English Læce for doctor] which contains a combination of Classical and contemporary English/British medicine. The anonymous compiler of the Leechbook (Bald being the extant tome's original owner rather than author) usually takes care to denote when a treatment or operation has Classical origins, which suggests that the majority of cures and treatments - in particular ointments, poultices, balms, salves and drinks - are contemporary Germanic or British medicine. It is this in particular which is often derided as 'folk magic', consisting as it does largely of herbal and plant-based remedies, yet the majority of these cures do in fact have a scientific basis and were recorded by doctors on the basis of a witnessed efficacy. Famously, one of the treatments in the Leechbook for an eye infection was recently shown to be effective in combating MRSA cases, but many of the herbs, plants or compounds prescribed for various ailments still provide the basic ingredients for modern medicines.

Witchcraft in a medical context is mentioned explicitly in a contemporary penitential, the Scrifboc, in relation to abortion, but this is most likely an active choice of language to underline the 'unnatural' nature of such an undertaking rather than an actual belief in any supernatural element.