You might need to turn a flywheel without a starter if you are setting the timing, or if you need to turn the engine over and the starter is either malfunctioning or is out of the vehicle for other reasons -- many jobs require starter removal, including transmission removal and repair. The only way to reach all the torque converter bolts is to turn the flywheel or flexplate.
Raise the vehicle, using the floor jack, then support it on jack stands.
Remove the access cover or flywheel cover, using the appropriate socket.
Fit the flywheel or flexplate turning tool onto the teeth of the flywheel or flexplate. Turn the engine in its normal rotation as far as needed. If you need to turn it more than is accessible, remove the tool and reinstall it on the teeth again, in the opposite direction from which the engine turns.
Make sure you know which way your engine normally rotates. If the engine's normal rotation is counterclockwise, and you turn it clockwise, you could knock the timing off, because the timing belt tensioner cannot keep tension on the belt. Likewise, if the engine's normal rotation is clockwise, do not turn it counterclockwise.