If you hear the , or feel with a helper turning the key, the starter solenoid pull-in, you have worn contacts and maybe plunger in the starter. Very common with older soobs. There are rebuild parts available. It is also very likely to be intermittent. Sometimes just whacking the starter with a piece of 2x4 a coupla times will let it start the car.
If the solenoid does not pull-in, then maybe bad N safety or even internally corroded battery cables ?