How to install new Window manager

[Guyren G Howe <guyren@geocities.com>]

I'm a newbie at this. I figured I'd get started learning to customise all
this stuff by installing a new Window Manager. I like the look of AfterStep
(one of its skins in particular), so I've downloaded all the relevant bits.

But I can't work out how to get Afterstep to come up instead of KDE. Can
someone tell me how to do this? All the explanations I've found go into
gorey detail about compiling it, then say something like "and then you
install it".

I'm also interested in the meta-question: where would I look, on the net or
in /usr/doc or whatever, to work out the answer to this question for myself?

TIA