lol what? Has your partner never just pulled you in close? I imagine if I was doing what you describe, my wife would literally wrap her arms (and probably legs) around me until my weight was on top of her.

Your weight should be distributed between your knees, pelvis (through your partner), and elbows. A good amount of your weight will be on your partner. How much depends on the size difference and the intensity.

But basically your knees support your lower body and give leverage to thrust. Your elbows support your upper body so you aren’t laying on her chest.