Look up the documentation for IceWM and that is where you should be able to find it. Additionally, a WM may provide additional capability - mapping key combinations to launch arbitrary applications, or providing a task bar and menu, like IceWM, or providing a number of Virtual Desktops, and so on.
Here is some information on IceWM, with some links for the manual too:
If this is what you are trying to do, then here is the answer:
ICE WM keys
Icewm allows launching of arbitrary programs with any key combination. This is configured in the libpath/keys file.
Here is the manual for IceWM:
ICE WM Manual