Intermediate switches are often used in a three way lighting arrangement, but because of their versatility they can be used for one way, two way switching, three way switching or even more intermediate switches can be used in a circuit which means you can use several intermediate switches should you need to.

This image illustrates how an intermediate light switch works (click to enlarge). You can see that in one position the contacts go straight through from L1-L2 and L1-L2 but once the switch is flicked the contacts cross over between L1 X L2 and L1 X L2

This means that an intermediate switch can be used for virtually any light switching domestic circuit. If you require just a simple on off switch you can use the top L1 terminal for the COM, then any of the bottom L2 terminals for the switched live.

To use an intermediate switch as a two way switch you can use one of the top L1 terminals for the COM, then use the bottom two terminals for what would be the L1 and L2 on a normal two way switch.
It may be necessary to use an intermediate switch as a one way or two way switch is a multiple gang switch is being used in a certain location, for example if you need a switch with 4 gangs (4 individual switches) and one of them must be an intermediate you would have to get a 4 gang intermediate switch and use the other three switches as one way or two way switches.