YaST => Software => Software Repositories => Click on "Add" => Select "Community Repositories" and click "Next"

 Repository Management in the Terminal

If you wish, you can manage your repositories via a terminal too. Add a repository with auto-refresh enabled zypper addrepo -f [URL] [Alias]. Example:

zypper addrepo -f http://packman.inode.at/suse/openSUSE_Leap_42.2/ packman

Disable a repository zypper modifyrepo -d [URL|Alias]. Example:

zypper modifyrepo -d Packman

Remove a repository zypper removerepo [URL|Alias]. Example:

zypper removerepo http://packman.inode.at/suse/openSUSE_Leap_42.2/

List configured repositories, showing details (priorities, URL, etc.):

zypper repos -d

See man zypper for more.

man zypper

Or for help on indvidual commands use for example:

zypper addrepo --help