(Ctrl-F: How do I use a "tripcode"?)
Basically to fit in, you find an anime character which everyone likes, typically some popular main character from a obscure anime, for our example, we'll use Miyuki from Lucky Star, then state your love for her as your (use 'mai' instead of 'my' to show you're one of the boys) pretend wife (waifu to fit in). then enter a hex or pound sign (#) followed by your social security number at the end to generate a random 64bit blow fish cypher pass to uniquely identify yourself. For example: Miyuki is mai waifu !ozOtJW9BFA
Once you've posted one time with your username/social security number, you just need to fill in your social security number in the name field every other time from then on and 4chan will automactically look up your saved username and use that. Your social security number will never be shown to the public, that is unless you skipped the first step.