On most distros, you should be able to plug in your USB camera and it should recognize it and load a driver for it automatically. You should then be able to start an application like xawtv and see the output of the camera right away.

On my distro, Debian, the drivers were no compiled into the kernel or as modules, so I had to do it myself. I first looked at the device and got the model number and manufacturer information from it, then I did a Google search for the device "manufacturer model# linux". I found that I needed the spca5xx driver. At this point I checked whether my distro included this driver by typing

apt-cache search spca

I found that there were a lot of binary module packages and one source package. The binary modules should work fine for most people, so you'd just

apt-get install spca5xx-modules.x.y.z; modprobe spca5xx

I happen to use a custom built kernel, so I need to get the source package and build the module against my running kernel. I use module-assistant to do this very easily.

module-assistant auto-install spca5xx

To find more information about module-assistant do a search for it on the PCLug page. Now we just modprobe it into the kernel and we are ready to go.