[rectang]

The mindset necessary for proofs is very different from how most people learn mathematics. So long as you can get a small preview of that mindset, you'll be ahead of the game. I'd suggest choosing a source which seems "too easy", or a curriculum which is "too short". It will be enough.

Additionally, as when learning anything mathematical, don't expect too much help from Wikipedia. Pedagogy often involves telling small lies to students at first, then clearing them up later. Wikipedia has a bias towards being correct, which means that the articles can't tell those small lies and the explanations are difficult for non-experts to understand.