Nose over in a plane with a tail wheel can be caused by a couple of things, the most common is that the main gear is too close to the C.G. and with the application of power the plane rotates on the axles rather than move forward. To correct just move the gear forward. The next most common cause is not knowing to hold full up elevator when applying power, and holding it until enough speed has been attained in the roll for the stabilizer to become effective.
Ground loop is caused by a loss of directional control during take off or landing causing the plane to veer very hard, and usually end up dragging a wing tip as it tries to roll over. The possible causes of this are too numerous to list, but the most common is not knowing how to use your left thumb for anything other than throttle.