The push up is a very basic exercise that most are familiar with and I would bet anyone that has ever exercised has tried to tackle.

Assuming a horizontal, face down position the subject uses the arms to raise and lower the body. The body should remain rigid as the subject presses upward until the exerciser has reached a position where the hands and toes are the only points of contact with a smooth line along the legs and back, arms fully extended. Hold for a moment, then slowly lower to starting position without bending torso or knee joints.

There are several variations on the basic push up, including one where the exercise is made easier by keeping the knees, rather than the toes, in contact with the ground as the arms are extended.

An even easier one that I have been known to use quite often is to stand a bit more than arm's length from a wall and lean to lay hands at shoulder height on the wall. By bending the elbows I will then let the weight of my own body lower me toward the wall, then pushing back out to arm's length.

Another variation on this uses a counter such as a kitchen counter to perform a push up against.

If you are a real push up pro then you might even try doing one armed push ups in which you balance on one arm for the motion, then after a certain number of push ups use the other arm.