No repositories are configured on your Linux SUSE server. You want to install packages. You cannot use zypper commands to install Linux utilities or other packages. You want to know how to you use SUSE direct address XML files to install packages. You think these XML files could help. When zypper commands fail because a repository has never been configured on Linux SUSE, how do you begin to install packages? How can you configure your server to work with a publically available (e.g. internet) server?
Run these two commands:
sudo zypper ar http://download.opensuse.org/distribution/leap/42.3/repo/oss/ openSUSE-Leap-42.3-Oss
sudo zypper se gcc
Now you are ready to install regular packages with zypper. (The second command above searches for a C compiler. You could search for a different package, but this one is common.)