yep,you need an amplifier and a instrument cable.Some older amps have lines in for mics I think,but its not common.For vocals,you might want to look into a small p.a system(public address system)...those are what you plug your mic into.

Go to a store and find an amp thats within the buget and is big enough for you.Most of all,get one that sounds nice...you can also look into some p.a equipment while there.Go in early and have someone help you with the ins and outs of music gear.

Good luck!