When I vote do I have to fill in all the different category , or can I just vote for a candidate for president?

You can vote for one person, or two, or the whole ticket. You just pick what you want, leave any you don't want to vote blank, then go to the finish part and click it.

You can just vote for President, but voting for your local electors is actually almost more important.

You can do what you like. With so many elections at the same time, remember they are all separate elections and you can vote in each one or not as you want.

You can vote for as many or as few candidates as you want.

Make it simple, don't vote.