Firstly welcome, your not an idiot it could happen to anyone, remove one rear wheel at a time and strike the centre hub of the disc to free off the handbrake shoes which are located inside the centre hub, rotate the disc until it runs free then repeat this procedure on the other rear wheel. The handbrake operates on the rear wheels only. As soon as is possible you need to have the handbrake mechanism and cables lubricated to prevent this happening again. It may also be worth removing the rear discs to enable servicing of the parking brake shoes.