You login as root at the login screen, no password needed. If you need to setup your partitions, do cfdisk for a more graphical program, or fdisk if you don't need it (I suggest you use cfdisk). Then just follow the program's options and answer its questions. You will not erase anything until you decide to write the partition table.

If you're finished, quit the program, and type 'setup'. That will give you a screen with options to setup your partitions (/, /home, /var, and so on), your swap partition, your keyboard layout, etc.

That should get you going. Then you just install (if you've got plenty of space, pick the full install, for most peoples, not only newbies, it's pretty hard to decide what programs are needed and which not) and reboot.

Login as root (again, in text mode), do 'adduser', and create a user account for yourself. No need to worry about the default shell and stuff, Slackware will set that up for you. Then do vim inittab, you'll get the inittab file. Press 'insert', move with your arrow buttons to the line that says 'id:3:initdefault' (the line above should say 'default runlevel'). Change the 3 to 4, press Esc, and then type :wq (that will save and quit). Then, just reboot (not needed but it's easier for you like that), and you'll get a nice login screen .