What kind of metronome is it? If it's a blue Korg I can help you with anything you need to know.
Once you turn it on it should start at a certain BPM (beats per minute)
there sould be buttons with arrows somewhere on there, that will raise the BPM or lower it. Best practice is to set it at around 80 BPM and just play your scales. Hit each note EXACTLY when the metronome clicks. Once you master that, boost it to 90 BPM then 100 etc.
For 8th notes put it at 60. and Play the note right on the click.. then when the dial is directly in the center (pointing at a 90 degree angle) and then hit the third note when it clicks again. So it will be 1 and 2 and 3 and 4 etc.