This is a quick and easy explanation of how to remove a garbage disposal especially a stuck one! The one in video has already been unplugged from the power as that step is #1 and plumbing trap/elbow also removed (you will need a catching pan for the stinky water.
https://www.boltsnutsscrewsonline.com/
Flat Head Countersunk Bolts, how to get the length.
Measuring socket screws, Countersunk Bolts