The bicep curl is an upper body lift that isolates the bicep muscle. It is a secondary lift which is done at the end of your workout after you have done the main lifts. The biceps have minimal responsibility in explosive movements or strength, so the purpose of this exercise is usually aesthetics.
To perform a bicep curl you can use a barbell, Dumbbells, bands, or a machine. Your arms should start almost completely straight and then bend at the elbows bringing the weight right in front of your face. Momentum should be kept to a minimum by trying not to sway your body or swing the weight up. Momentum will decrease the amount of stress placed on the muscle.