I really want to buy a capture card for my birthday! Wich one should I buy? And also, how does it work when you use a laptop?

Buy a GV-USB2, cheap, effective. I use it on my laptop.

Do I need to get something else? (Cause, I have the n64, I have the game, I have a modern Tv, I know what capture card to get, and I know that I have to use OBS and Livesplit)

First, get a CRT, that's super important imo. Obviously you can get used to 1 - 2 frames of input delay but i wouldn't recommend that. Get a GV-USB2 they cost around 30 - 40$ and take a little longer to arrive unless they are sellers from the us.

i got a easycap but it didnt work idk why