Any doc with "v1" or "v2" at the end of the name is probably not the "real" document you are looking for. As for why: MediaWiki, the current documentation platform, doesn't have a built-in way to hide old documents without deleting them entirely, and a search will therefore sometimes pull them up (ironic--as bad as default MediaWiki search is, it's sure great at turning up these). All the "v1" docs I'm aware of are from 1.x. platform versions. Version 2.x, which has been around for a long time now, introduced a UI overhaul, and most docs were re-written for that, some in a staged "v2" form, then merged into the "regular" doc--so that is generally the one you want.
Given all that, the best way to use the current docs site is to follow links from the home page, other pages, or the Document List--or the built-in app help links in the UI, links you get from others, etc.
I can't speak to why it was all done this way, aside from the documentation platform oddities I mentioned above, but I can tell you there should be improvements coming soon. I'm not sure if I'm allowed to say more. Thanks for the feedback!