Political Questions

I usually blog about words, books, and kids, so I hope readers won't mind that this post is off topic.
I've been thinking about politics lately for obvious reasons and have some questions.

Why do political parties exist at all? I don't think the Constitution mentions them, though it has been a few years since I took the Constitution Test in 8th Grade.

Who decided that seats in Congress should be arranged according to the political parties of members? Is that in the Constitution? If not, why not eliminate it?

And, why do the parties get to nominate candidates for the presidency? But, if they didn't do it, who would?

And, what about the Electoral College? Who decides who the members are? And what would happen if those members chose to vote differently than the majority in their states? If they can do that, then they have immense power and the USA isn't actually a democracy. 

If the Electoral College were to be abolished I guess we'd have to wait until every single vote had been counted to know who won elections. This year it would have taken weeks for us to get the results.

And why not count our votes according to the individual citizens instead of involving states at all? That way every person's vote would count the same.

I'd love to hear your answers and comments on these questions. Thanks.