Examine the external jacks of your microphone and amplifier. Most amps have a 1/4-inch input jack, and most microphones have a three-prong output jack. The type of input and output jacks will dictate the type of cord you need.
Purchase a microphone cable that will allow you to run your microphone through your amp. If you have a three-prong microphone jack and a 1/4-inch input jack on your amp, you can purchase an XLR to 1/4-inch cable. If you already have a microphone cable, and it's an XLR male to XLR female cable (one end has three prongs and the other end has three small input holes), you can purchase an XLR connector. One end of the XLR connector will have a three-prong jack, which attaches to the mic, and the other end will have a 1/4-inch plug that can be inserted in your amp's input jack.
Plug the three-prong jack into your microphone, and plug the 1/4-inch end into your amp. If you purchased an XLR connector, plug the three-prong connector into your existing microphone cable and the 1/4-inch end of the connector into your amp.
Turn on your amp and experiment with the settings. Depending on your microphone, you may have to increase the main volume and experiment with the gain, treble and bass settings.