Slackware is a distribution of Linux just like RedHat, Mandrake, Debian & a whole lot more are out there. Distro's are where someone took the Linux Kernel and added the things that they felt were needed to get the job done. Some distro's are for Servers, some are for Workstations, some are easy to setup & use & some are hard to setup & use. You need to search the web & the distribution forum here & decide for yourself which one is right for you. WindowMaker is a GUI (Graphical User Interface) just like in Windows you have a desktop with wallpaper & icons. WindowMaker, Blackbox, IceWM are some lightweight windowmanagers (don't hog alot of the systems resources) KDE, & Gnome are heavier (use more resources). All the windowmanagers & distro's named here are just a small sample of what is out there. Search the forums here, do a WWW Google search read any & everything you find about Linux. There are endless choices out there you can design your own distro our use one someone else has compiled.
My first Distro was Vector Linux 1.8
http://www.ibiblio.org/vectorlinux/index.htm
it is Slackware based & isn't to difficult to install and learn. I am currently running RedHat 7.2
http://www.redhat.com/ It was a little bit harder to learn but it is widely used & there is alot of info available for it. I want try Mandrake next
http://www.mandrakelinux.com/en/ I hear that it very newbie friendly.
Hope this helps
Bubba169