Film photography could seem complicated but it is not. There is only one variable: light.
Just how human eyes work, you can’t get photos or images without light. Every setting on your camera are ways to expose your sensor (film or digital) to more or less light. I can’t stress it enough, light is king.
The shutter speed allows the sensor to be exposed to light for a certain amount of time, while the aperture exposes the sensor for a certain amount of light. The sensor sensitivity is the last important setting of the exposure triangle.
If your shutter speed is high, the sensor is exposed to less light. If your lense is wide open (
aperture’s stop ≥ ƒ/16), the sensor is exposed to more light. Your sensor’s sensitivity is the only setting that can’t change in film photography
How I expose film
No matter how I expose my film, I tend to develop my film for the superior stop of exposure value. If I shoot Tri-X as it is rated (400 ISO), I’ll develop it for EV+1: 800 ISO.