You put the film back in and keep the lens cap on and put something over the viewfinder window usually found on the camera strap and cycle the camera through until you are one frame over where you left off on the film. e.g. if you took 10 shots on a 36 roll, then you would move it along until you advanced ti 11 frames. This allows for not getting it back in the same spool socket and gives a little leaway to the film so you don't expose over an image already taken.

Does that make sense to you.