Posts on the Front Page got there by being voted on when on the "newest" page, there is (almost) no other way of getting there. So everything you see on the Front Page was once taking its chances on getting noted on the "newest" page, and succeeded. And to answer your question, I always visit "newest", and if there's something there I like, or that I think is informative, useful, or relevant, then I upvote it. There…
No. If someone submits a link that’s been submitted recently their submission upvotes the original. I’d wager that that’s how most links hit the front page.
[1] I don't remember the official name. The explanation by dang was linked in other comment. I'll copy it here https://news.ycombinator.com/item?id=11662380 The details are part of the secret sauce, so the details may have changed.