So easy you will kick yourself
start Yast from the menu. It will request the root password enter it
then Software-Software Management
Search for gcc. You will get lots of hits you only need the main gcc package for most things unless you are a developer that uses Fortran or some other compiled language.
Check it then install.
You probably should add some additional repositories. (Suse software supply sites with pre-compiled packages for Suse)
Also done in Yast. Think of Yast as being the what Windows control center should have been.
Also I hope you really did not give you normal user name root privileges. A very very bad idea. This is one of the main things that makes Windows a major target of malware and protects Linux machines form the same.
You do not want to normally run as root or with root privileges.
Here is some pages that will help you with additional repositories
Repositories - openSUSE-Community Additional YaST Package Repositories - openSUSE
You will want at least Packman for multi-media stuff