How does this work as far as the candidates for the presidential election?

I’m looking at this link. Are all the people listed actual, viable candidates (with the except of those who have withdrawn, of course.)

And how would that work at the ballot? There are 30+ independent candidates. Will they each be listed on the ballot?

Same with all the democratic & republican candidates. Will they all be listed on the ballot? I guess I’ve never really paid that close attention in the past. I always voted for one of the top 2.