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=4.6.3 ./nvidia-legacy390-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, move 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.