Bitcoin Mining is no longer viable using off the shelf consumer hardware. Unless you have hardware specifically designed to mine Bitcoins ("ASICs"), it is not worth doing under any circumstances. At best you might make a dollar in a few months. But more likely you will just be burning up your hardware and never receive anything for it because the hardware is too slow to reach the minimum withdrawal level.
Mining Bitcoins requires special software known as a Bitcoin Miner. BTC Guild recommends cgminer (or bfgminer) for serious miners.
After you register on BTC Guild, you have a single worker created automatically, named (username)_1. Workers do not require passwords to mine at BTC Guild. We recommend entering '123' as your password when connecting, since some miners do not function without a password
If you run multiple computers ("mining rigs"), we recommend that you create a new worker for each computer. This will make it easier to monitor your computers through the BTC Guild website and identify possible problems.
How to Connect: CGminer/BFGminer
Due to the various settings of different ASICs, BTC Guild no longer provides specific instructions on how to connect. If your miner has a web/GUI interface, you should be able to simply input the connection information above to connect to the pool. If your miner requires CGminer/BFGminer, you should consult your hardware provider or the BitcoinTalk.org forums for specific directions/flags which may be required.
There is an in-depth guide on how to connect using USB Block Erupters in its own section (link at top of this page). While some of these steps may not be needed anymore, some parts of that process, such as creating the shortcut and adding custom flags, may still be helpful for other hardware.