All right! Finally, someone better than this "Isai" guy! I'd be honored to be taught at your feet, my lord.
download Project 64k. Download a SSB 64 US version ROM (google for both of those) If you've got Vista or 7 on your windows computer, download Jabo's 3d8 plugin and rename it 3d7 and replace your old one with that and you should be good. Buy an N64 to USB adapter (google is your friend there again) and plug your controller right in, or else just play on Keyboard.
From there, start up the netplay, join "The galaxy", and ask for a game. The first English-speaking person who joins will almost certainly beat you. Badly.
More in-depth stuff is in the Index thread that peeps have linked you to. If you've got specific questions, post them in the "Ask a question, get an answer" thread and we'll be glad to help you.
It's surprising how many guys who show up on this forum for the first time are the best in the state/US/world.