If you are new you'l be better of with kde or gnome desktop.
In these two you can easily change the desktop and the resolution.
You should choose one of the two. Debian has very good docs on its website. You have to read a lot and to learn. It is the same way as by win without learning how to, you don't get anywhere.
From there on you can use apt to install krusador that is a kind of file handling program like norton commander under windows.
You can copy , delete, move whatever you want.
Before you install read the docs, to which map it is installing in my Suse 9.3 system it was /root/.kde/shaer/apps/kicker and then you connect it with a nice icon to the dekstop.
There is nothing wrong with windowmaker, but I think most people use Gnome, KDE or the Console. I have tried it a long time ago, but I don't remember much of it. KDE is like windows, Gnome is a little bit different more structured, if you worked with dos, you can work also withe the console. But for all three you have to study first...................... a lot.
Screensavers - KDE as well as Gnome have a lot of them build in - you can also Google.