I can't tell you much about the medieval bards in continental and British Europe, but in the norse and viking societies, the bard was a important figure.

In Scandinavia (and by extension Iceland, Orkneys, Faroes and parts of Britain) the bards were called "skald". The original etymology is unknown, but later it became synonomous with poet.

These skalds were poets for hire. Mostly for lords and kings, to whom they sang the "history" of this person in a verse. It's important to note that this was not written down, and were carried on in oral tradition until the 11^th century, where Christianity brought the latin alphabet.

Because of the aforementioned, we have little left of what is assumed to be a plethora of different kvad (songs) and know only of a handful of skalds. The most famous one is "Snorri" (Snorre Sturlason) whose kvad heimskringla is known as the most important piece of literature in Norway (apart from the constitution, of course). However, he wrote his kvad in about 1220, and his motives were the viking age. His works are therefore influenced by the christianized society. However, it is still viewed as one of the most important literary sources of viking society, together with [Möðruvallabók}(https://handrit.is/is/manuscript/view/AM02-0132).

The poetic Edda whose author is unknown, is one of the most important sources of religious literature, although this is also written after christianity came to Iceland.

Sources (sorry, all in norse or Norwegian due to me being away from a library right now)

Knut Helle, Ståle Dyrvik, Edgar Hovland og Tore Grønlie: Grunnbok i Norges historie. Fra vikingtid til våre dager.

Sverre Bagge Europa tar form : år 300 til 1300

Odd Einar Haugen Norrøn grammatikk i hovuddrag

http://heimskringla.no/wiki/Forside (a collection of texts and sources from all of the nordic areas, mostly pertaining to skalds and their kvad)