Short Answer:
There are two (possibly three) different Licenses you will be dealing with.
The first is the server license. Every Win2K server must have one.
Second, there is the Server Client Access License (CAL). There are 2 different licensing modes: per-server and per-seat.
Per-server: each concurrent connection to each server requires a CAL.
Per-seat: each client computer requires a CAL regardless of how many servers are being accessed.
Unless you are operating in a single server environment (in which case it really doesn't matter which mode you use), it is usually more economical to use the per-seat mode. You are not required to use the License Logging service provided by Microsoft. In my experience, it usually creates more problems than benefits.
The third possible license you will use is the Terminal Services Client Access License (TSCAL). If you use Win2K Terminal Services in Application Server mode, every client that accesses Terminal Services requires a TSCAL in addition to a normal server CAL. However, Win2K and WinXP Pro clients do not need TSCALs as they have them built into the OS.
How it works: There is nothing that you need to install to make the Licenses "work." All it basically is,is a piece of paper that says you have X number of licenses of a certain type.
Hope this helps.