Highlight on dark brown hair

Regarding your other post, you could go darker or do funky colors temporarily (but not bright funky colors because you have to bleach first to get those to show up, and that would not be temporary).  You cannot go lighter temporarily because that requires lifting the pigment out of the hair, and that is not reversible. 

If you just want brown highlights and don't care if they're temporary, just go to a salon and let them do them for you.  They can always dye them back if you get sick of them, but I wouldn't suggest doing it yourself if you're new to dyes.  To do them yourself requires a little knowledge of how the chemicals work together.  If you would like to learn all of that, read Claude's sticky at the top of this board for great background info, and be prepared to try a few different things on test strands before you do your whole head.  If you don't want to get into learning all of that, just go to a salon, they can give you highlights, no problem.