You need instructions on how to use a drill?
but yaeh, that's the clutch...controlsl how much torque is applied.  Essentially the clutch will "slip" at a certain amount of torque.  you can play around with it by holding the chuck with your hand on the lowest setting and you'll hear it click - that's the clutch slipping.
the marker that looks like a drill bit means "no clutch" and is normally used for drilling instead of screws.