Can someone explain the modules system?

Modules are pieces of the kernel seperated into loadable pieces. The benefit is that you can reduce memory usage by not having a feature loaded into the kernel at all times. You can then load the module if that feature is needed.

In many versions of Linux, you can use modconf to easily insert or remove modules. Slackware may need to use

insmod .

To remove a module, use:

rmmod

substituting the module filename for of course. You can find alist of modules in /lib/modules//.

To compile a feature as a module, select type M or Module for the install. Use make modules ; make modules_install to compile and install the modules...

Hope that helps

The other person's answer is pretty accurate, I just feel the need to add mentioned of the /etc/conf.modules files which is often used to set up relations between things like ethernet cards and modules with "alias" lines...

alias eth0 3c959 (a random 3com NIC identifier)

Go to:
http://ctdp.homestead.com/files/linux/usersguide/index.html
There is a section on the kernel that talks about modules, where they are, and the tools that are used to install them. If you need more details, you should be able to read the man pages on the various module tools.