The best resources like this are journal archives. I use JSTOR and GALILEO. Both have a fairly good search function, as well as acces to a number of different journals. Neither however is free, nor can anyone add content to these platforms . They're heavily peer reviews and academic in nature. JSTOR I believe anyone can pay for, but GALILEO is exclusive for those who have attended institutions in Georgia, USA.

Outside of journal databases there are archives. Archives are almost all state run, (though while I haven't heard of many private archives of note they do exist) but are free to both public and private interests. Anyone can donate quality articles to them as well. The definition of quality will of course depend on the article and archive its being donated to. The British archives most certainly would be interested in say your great grand uncle's letters from his time serving in the colonial administration of India, after some verification. They would not be terribly interested in his coat and pistol, (though the Royal Armory might) nor would they have much if any interest at all in your own writings on your grand uncles letters.

So if you want to learn, look for journals in JSTOR, or visit whatever archives are near you for primary source documents.

Contribution however is a bit harder, and unless you're currently enrolled in a higher learning institution, or have attined an advanced degree, there is very little interest in your contribution.

The best places for someone who wants a more-than-popular view of a given historical subject or topic are not journal articles (which are frequently niche and argument-based) or databases (of any sort), but the kinds of synthetic secondary or even tertiary sources that historians occasionally contribute to that are sort of in between "edited volumes" and encyclopedias. Things like the Cambridge Histories series are what I have in mind. These are scholarly volumes written to scholarly levels of rigor (and citation) that are meant to give overviews of the scholarship on any given subtopic of history. So for example the Cambridge History of Science contains many sub-volumes that divide up the period; the first volume is on Ancient Science and contains 30 articles written by scholars in the field covering specific subjects ("Greek Mathematics," "Greek Mechanics," "Astronomy and Astrology in India," "Mathematical Knowledge and Practices from Early Imperial China until the Tang Dynasty," etc.). The articles are written in order to bring any scholar reading on this up to speed very quickly, and usually are written with historiographical disputes in mind ("Scholar X argues for one interpretation, but scholar Y argues for another"). Each volume also has an Introduction that frames the entire subject and gives one sense of how to navigate it.

There are presses other than Cambridge that do this as well (Oxford is another, though theirs is not as extensive as the Cambridge ones). Anyway, this is the sort of resource that is most analogous to what you are talking about. It is often overlooked by the general public entirely because it is not really aimed at them. But this is how many historians themselves get up to speed on a topic, especially if we have to teach a lecture on it and it is not something we actively research (and we do not have time to read five books on it, which would be the better way, ultimately).