webserver, I'm assuming you mean http server (apache). If so, with slackware it's a piece of cake. You install the Apache package, edit the /etc/apache/httpd.conf to your taste's start apache:
apachectl start (might just be apache start) and that's it. Depending on what you edited, your apache default page might be /var/www/htdocs/index.html.en
Yes, you will need to add accounts for your users, how do you want them to access the server, via ftp or ssh or both or something else? Slack comes with ProFTPD which, again, is as easy as install, edit /etc/proftpd.conf to your tastes and start the server. Postfix I downloaded and installed by reading the README/INSTALL file in the package, and set it up just about as easily. Really, slack is so well documented that it's not bad at all.