Search and install SlackBuilds. More information: http://slackermedia.info/handbook/doku.php?id=slackbuilds.
sport
for the first time:sudo mkdir -p /usr/ports && sudo rsync -av rsync://slackbuilds.org /slackbuilds/$(awk '{print $2}' /etc/slackware-version)/ /usr/ports/
rsync
:sudo sport rsync
sport search "keyword"
sport check package
.info
files of a package:sport cat package
sudo sport install package
sudo sport install $(< path/to/list)