Find 'em: You'll find these deceptively valuable pieces of metal in containers throughout the wasteland, so if you're out "prospecting", keep your eyes open. Also, if your in desperate need of caps, pick anything up, tin cans, empty bottles, or pencils, pick them up and sell them for your money!
Earn 'em: If someone pays you to do something for them, don't question their motives! They'll pay you in caps, so step to it and you'll be raking in the dough in no time.
Steal 'em: There are, of course, less legitimate ways of obtaining these shiny little caps. Everyone carries them, so if you're quick and careful enough you can "accquire" a few extra caps. However, most people keep the majority of their savings locked up, so if you're good with a lockpick or computers you should be able to "liberate" vast quantities of bottlecaps from their current, undeserving, owners. And remember you can't sell them at the city you "aquired" them, you have to go to another city.
Spend 'em: So what now? I hear you cry. Well, now you get to do the fun part: Spend! Spend! Spend! From buying clothes at Potomac Attire to bargaining for strange meat from those dodgy looking hunters, everyone accepts caps. As they are the only accepted legal tender in post apocalyptia, the more you have, the less unbelievably horrific your life will be.
Haggle 'em: Whats that ? Getting less caps than you should for an item ? Welcome to Bartering my friend! The Barter skill is unbelievablyuseful to you and your pockets. The lower your Barter skill, the lower the price you will get for your unwanted goods. Naturally, increasing your Barter skill will mean you will get more caps for your items, so make sure you use your skill points to increase it !