https://guides.brit.co/guides/make-chainmail-jump-rings

You can do it with a hacksaw, but it's going to be a nightmare to get a reasonable amount of them. It's a good starting point.

Usually people use a specialized machine, often powered by a regular drill, to coil and cut them all in the same spot. More advanced ones also collect the dust, which can be important for valuable metal like silver and to save your lungs.