Mining bitcoin and mining most of the altcoins are two different stories. I have no idea exactly what side of mining you are interested in, but here are some hints:
For bitcoin, you would need specialized (read, expensive) equipment (ASIC). The time for mining bitcoin using "normal" hardware found in an average PC is long gone. Check out, for example,
this thread to get an idea what I'm talking about. (Hint: there are linked images, follow them to see exactly what kind of setup is required).
For most of the altcoins, (depending on the coin and their hashing algorithm) you can still use PC hardware. Primarily I am talking about high-end graphic cards (GPUs). Ideally, you would need several GPUs in a rig (the more you can afford the better). Check
this thread for more information. Even just one high-end NVidia or AMD graphic card can be enough for some coins, but in that case the profitability can be rather questionable. Note: "Some altcoins require ASIC as well, for example LTC or scrypt-based coins".
In either case, you would have to join a so called "mining pool" and try to mine coins together with other participants in the pool (and share the profit), because nowadays it is virtually impossible to
solo mine any coin (or should I say any coin that means anything).
