This is a sixteenth note. It lasts for one quarter of a beat. There are four sixteenth notes in one beat. There are 16 sixteenth notes in one bar of * time.
As with any new note value, it is important to practice your scales using 16th notes until you are comfortable with them. Here is the C Blues scale played in sixteenth notes over two octaves. Take it slowly at first, and remember to use your metronome and count out loud as you play.