Go to
http://slackware.com/getslack/ and choose a mirror close to you, such as:
http://ftp.scarlet.be/pub/slackware/
There you'll see subfolders for each version. Go into the /slackware-9.1 directory (for Amigo-2.0). There you'll see subfolders such as /pasture, /source, /extras and another one called /slackware. Go inside this last one and you'll see the standard Slackware package subdirectories:
/a (base packages)
/ap (useful command line and system apps
/d (development programs -compilers, etc.)
/l (system libraries)
/n (networking progs)
/x (X11 system)
/xap (X11-based progs)
There are other subdirectories also, but these are the main ones, unless you want KDE or GNOME.
Sometimes source-code comes as tar.gz. Unpack the archive with:
tar -xzvf filename.tar.gz
or:
tar -xjvf filename.tar.bz2
A tar.gz archive is exactly the same as a .tgz. And a tar.bz2 is the same as a .tbz2.
Slackware packages are delivered as .tgz archives, but don't think thta ll .tgz's are slack packages.
Always read the README inside the archive, and the INSTALL file. If you see a file called Makefile inside, then you have source-code package and will need to install the compiler and a few other things, and learn to compile. But much of what you want is available pre-compiled by looking around.
Take the programs one at time and ask for help here, or on the slackware forum.