ISO rating on the film.

[MattKing]

My advice to you about diffraction induced by using smaller apertures with lenses for 35mm cameras is to ignore the problem (for now). The effect is quite small, and the extra flexibility you enjoy by having those apertures (f/11, f/16 and f/32) available to you is much more likely to be of benefit to you and your photos than the tiny, tiny bit of reduction you will see in resolution and contrast. I only worry about diffraction induced by using smaller apertures when the film, the light, the needed depth of field, subject movement and my use of a tripod permit me the choice of a wide variety of apertures.
Film is too much fun to obsess on that particular detail - at least at the beginning stage of learning!
If you want to see where the effects of diffraction induced by using smaller apertures starts to actually matter, look up pinhole cameras - f/295 isn't unusual!

 

[lxdude]

Matt King has given you some very sound advice there.
Remember, there's a reason the lens can be set to those narrower apertures-sometimes the benefit of using them outweighs any loss from diffraction. Learning good hand-holding technique and using a tripod when you can will do more to ensure sharp images.
Remember also that most lenses are not at their best at their widest aperture either, but using them at their widest aperture gives you the ability to produce images you otherwise couldn't.
Experiment, learn, and enjoy the whole process of discovery.