I think OP is talking about a partitioning issue.
OP, FYI, "C" is not used as a drive label in Linux (If that's what you were talking about)
If you're not dual-booting [i.e. if Slackware will be the only OS on your 'puter] then you can just have the Slackware installer do the partitioning automatically.
TIP: Print this out before installing Slackware: http://docs.slackware.com/slackware:beginners_guide
It tells you how to configure your system after installation- very important.
Also, there are some great videos on Youtube- especially the ones by LARathbone, on how to install and configure Slackware.
I'm a Slackware noob myself, and I found those videos invaluable!
You'll love Slackware. It has none of the bloat and BS that modern Ubuntu versions have. It works better than any distro I have ever tried. Configuring it can be a little work, especially for us noobs- but between the documentation I linked to above, and the Youtube videos, it's a piece of cake.