This is the kernel-module needed by the proprietary binary nvidia driver.
You also need the nvidia-driver package from SlackBuilds.org.

To build the package for a kernel different from the running one,
start the script setting the KERNEL variable as in
    KERNEL=3.18.19 ./nvidia-kernel.SlackBuild

A default config file is placed at /usr/share/X11/xorg.conf.d/10-nvidia.conf
to make sure that X loads the nvidia module.  If you need to make changes, 
copy that file to /etc/X11/xorg.conf.d/ and edit the copy.  You do not need 
this file at all if you have a proper and complete xorg.conf.

The xf86-video-nouveau-blacklist package from /extra is required.