In Slackware you can see your installed packages under /var/log/packages. If Samba is not there you need to install itr either from cd using pkgtool or get it via swaret or slackpkg. (see readme/manpage of appropriate program on how to use it) I am affraid you can't check wether progerams compiled from source are present in an easy way. You just have to search you system for the program using slocate for instance.
To configure Samba you can either use the SWAT webconfig tool or you van manualy edit the config file (/etc/samba/samba.conf).
To use SWAT you must first uncomment the appropriate line in /etc/inetd.conf which looks like this:
swat stream tcp nowait.400 root /usr/sbin/swat swat
Then you can use your browser to configure samba by opening http://localhost:901
You can also use SWAT to check the status of your Samba server
O'Reilly has written a great book about Samba I believe it is available for free download.
U can use it to figure out what all the options are in the config file