Shoulder push-ups are pushups with your hands at a distance that is shoulder-width.

Standard push-ups use hand spacing that is slightly closer than shoulder width.

Elevated push-ups are with your feet elevated 1 to 2 feet off of the ground. The higher the elevation, the harder it is.

Seated Leg tuck ... hmmm ... Sit in the edge of the bed/bench. Get yourself into the "up" position of a crunch. Your legs should be straight out (yes, they are suspended in the air). Now, bend your knees at a 45 degree angle. Now, Pull your legs in toward your chest. That's a seated leg tuck. Works the lower abs, and the uppers get a static contraction workout.

your arms can hold the edge of the bed/bench for support, but not to help you do your reps.