1: Shop vac out the water & Goo,.... or just undo the trap over a pan or pail & drain it.
2: Test the disposer. There is a breaker button near the edge, Push it & turn it on. Even just a moment of hum says its OK.
3. It is attached to the sink by a bayonet ring. The three tubes use a special wrenck, or any screwdriver that fits. Unscrew it (1/3 turn). If the thing is still attached to the trap, loosen the nut & lift it free & away from the sink.
4: Lift off the "splash guard" and reach inside ^ work out the jamming piece. A wrench, or allen wrench will help, forcing it to rotate & free up.
PS: NEVER use Drano or other silly (but dangerous chemicals which plumbers HATE!)
A disposer that is jammed or not run a while will always "plug up" and not drain, but any turning of the grinder (what the wrench is for) breaks the seal and lets it drain!