The Polaroid 100 camera has an automatic Electronic shutter that needs a battery. As you are holding the camera, your left hand is around the battery compartment. Pull the front of the camera back and the battery will be exposed.
IIRC it is a 4.5 V battery Duracell PX-19. It has special snap connections at each end. I haven't priced one in ages but I'm thinking $10 or more. I have heard of AA cells being connected with a holder or soldered in series that worked fine.
Once you have a good battery you can check the shutter without film by firing the shutter while looking through the back at different light sources and listing for a delay as the shutter opens and closes.
Good luck with your new camera, just remember to set the film speed under the lens and then tell it where it is in the windows on top of the shutter.

Francis in VT