To a beginner, how to properly grip a golf club can be one of the biggest obstacles he'll encounter as he starts on his golf journey. After all, the position of the thumbs and the interlocking of the pinkie finger with the pointer finger are just unnatural to a first-timer. Once the grip itself is perfected, the job isn't finished. There are a variety of nuances that need to be understood when gripping a golf club, some that extend well beyond simple hand position.
The interlocking grip, while unnatural feeling at first, is fairly easy to pick up. Start by taking the top of the grip in your lead hand (this is the hand closest to the hole). The shaft of the club should run through your lead hand, from the base of the pinkie finger to a place between your second and third knuckle on the pointer finger. Your thumb should be running down along the top of the shaft toward the club head. The thumb shouldn't be exactly straight down but running off toward 1 o'clock for a right-handed golfer. Bring the non-lead hand down below the lead hand, sliding your pinkie finger between the pointer finger and middle finger of the lead hand. The thumb of the non-lead hand should be pointing down as well, the ball of the thumb going over the top of the thumb on the lead hand.
The ten-finger grip is a good, basic learner's grip. It's great for creating leverage with your clubs but has the disadvantage of lower clubhead speed. The basic difference in the ten-finger as opposed to the interlocking grip is that there is no interconnecting of the two hands on the club. Once again, the club is held in the palm of the lead hand, the shaft of the club running from the base of the pinkie finger to a spot between the second and third knuckles on the pointer finger. The non-lead hand comes from the opposite side of the club and wraps over the thumb, in much the same way as the interlocking grip. This grip is a good alternative grip for children. The only caution is that your hands, because they are not interconnected, tend to slip apart.
The overlap grip is an alternative to interlocking your pinkie and pointer fingers. It's commonly used by people with larger hands, where the process of interlocking fingers presents problems. The essential grip of the club is the same, with the shaft running down between the base of the pinkie and between the second and third knuckles of the pointer finger on the lead hand, then across the bases of your fingers on your non-lead hand. The difference comes in that you take your non-lead hand pinkie and place it on top, between the pointer and middle fingers of the lead hand. Smaller hands may have a hard time finding a comfort zone with this grip, the non-lead hand tending to move around on the shaft, throwing your club head position at ball strike off.