A nosepick is a manouvre in bicycle trials where, with the front brake locked up you shift your weight forward and balance on the front wheel with the back wheel in the air. More commonly it is performed by locking up the front wheel while moving forwards. If you're trying to learn to nosepick, don't do it on pavement. Endoing (falling over the handlebars) is more fun on grass than on pavement. Although, if you're just starting to learn you're probably not going as high as you think, so don't worry too much.
Nosepicks are used for various moves like 360 drop offs (AKA helicopters) and nosepick sidehops. To see an example of a nosepick look around for a bicycle trials site with videos such as www.trials-online.com or attend a competition.