Standard
This is the method to use if you want to build a character in the typical way.
Quick Build
A way to get a play-ready 1st level character (that's optimized according to the PHB guidelines) fast.
Randomize
This will either make a completely random character (level, race, class, background, spells, etc.), or you can specify a few of those parameters. Keep in mind that these are completely random - this method will not create a necessarily optimized character. It might be fun to play with that kind of randomness though!