Plenty of disposal call-outs turn out to be something you can put right yourself in a couple of minutes, so it is worth a try first.
Start here
If it hums but will not turn, the motor is fine and something is jammed. Switch off the power at the wall, use the small hex key that came with the unit to free the flywheel underneath, then press the reset button on the bottom. If it is completely silent, the reset on its own often does it.
Older kitchens and cast iron drains
Fitting a disposal to an old cast iron drain in one of the original Hanahan homes sometimes uncovers the real issue — a line already narrowed with buildup that cannot take the extra load. If a new unit causes backups straight away, the drain is the problem rather than the disposal.
When it really is finished
Water coming from the body of the unit rather than the connections means it has rusted through and cannot be repaired. Repeated tripping after a reset means the motor is going.
What it does not deal with
Cooking oil and fat. They go down warm and set further along the pipe, and with hard water scale already narrowing those lines, that is the usual reason a kitchen drain here keeps blocking.