What is a stop?
Measurement of exposure based on shutter speed, ISO, and aperture.
How does aperture affect the depth of field, and how is that calculated?
When there is a higher aperture, the lens is more open and therefore can focus in more.
What are some considerations for slow shutter speed, and how does focal length affect this?
You should consider your aperture and ISO when determine shutter speed.
When should you use a shallow depth of field?
When you are trying to focus on one small object as your main object in the image.