I don't know SuSE very well.
These days, modern distributions include the option of sharing the connection right from the install.
If not, you might wish to read about DHCP server (not really necessary, but I preferred things that way),
(proxy) DNS server unless the DHCP gives the ISP server address to clients. I used MaraDNS.
And a Firewall/packet forwarding package, basically I used shorewall to easily set up IPtables.
You should find some info on those packages quite easily.