You have a Parker Hale steel silencer. You should have a stack of baffles, plus two flat washers and a short piece of spring.

Ideally you need a length of rod and stack the baffles onto each other so the slightly curved base piece sits in the first baffle and then just add all the baffles in the same manner. Then add a flat washer, followed by the spring section and then the final washer. Slide these into the body of the silencer and then screw down the cap.

You can do it with out a rod but it's a faff.