Professional audio equipment can be extremely expensive. Even cheap public address (PA) systems tend to cost at least $200. Sometimes spending this money just isn't practical, especially when you are starting up a new band or simply delivering a speech at a relatively small gathering. Instead, you can create a makeshift PA by plugging a microphone into a guitar amp. The act of plugging your microphone into your amp will depend on the type of plug at the end of your microphone.
Examine the plug at the end of your microphone. If it looks like the plug at the end of your guitar chord (a 1/4 inch jack) you can plug it straight into your amp. If it has a larger plug with three visible metal prongs on the inside it is an XLR connector. You will need to buy an XLR to a 1/4 inch jack converter to plug it into your guitar amp.
Buy a converter piece if needed. XLR to 1/4 inch jacks can be bought at most music and electronic stores. In the rare case that your microphone has an 1/8 inch jack, you will have to buy a 1/8 inch to a 1/4 inch converter.
Attach any converter pieces necessary and then plug the 1/4 inch jack into the input on your guitar amp. Make sure the microphone is turned off before turning on the amp.
Always use your clean channel when running a microphone through a guitar amplifier. The distorted channel has a tendency to feedback terribly when a microphone is run through it.
A microphone run through a guitar amp will work, but it will not sound very good or get very loud. If you find yourself using your guitar amp to frequently amplify vocals, it may be a good idea to invest in a PA system.