Download a package from one of the slackware mirrors, for example vsftpd
and install one of these with the installpkg command to get ftp up quick. The packages linked above are for 11.0 btw.
If you want to compile you'll find a readme file in almost every souce archive telling you exactly what to do, as comprookie2000 already mentioned.
You'll come to the point where you really need or want to compile something when using slackware for a while, believe me
And there's probably easier things to compile for the first time than an ftp program...
Nevertheless, congrulations for your fine choice of a distro