Linux admin notes - kernel modules
Shell, admin, and both:
Modules are can be used as kernel code, loaded and unloaded at runtime.
Ideally you'll never have to deal with them in general admin; if they're necessary and present they will often be loaded automatically.
Some people who compile kernels prefer to compile any and all drivers as modules instead of baking them into the kernel, so that you can reload and replace them without rebooting.