If Ubuntu has sudo apt-get to the server around the world for updating the package, slackware has also the server like that. Just use slackpkg to install some program or package.
To start it, open your console, become root user with su
#slackpkg install mysql (for example)
but first let’s edit /etc/slackpkg/mirror to define the server. I am using kambing server, cause its nearers from my place.
Add http://kambing.ui.ac.id/slackware/slackware-current/ to the bottom line of the file. And run slackpkg update