The OBS web interface can be used to setup OBS, browse the content and to build packages. It is also the api url to be used with clients like osc.
The OBS repositories contain the build results, the repositories can be added to package managers like zypper or apt.
The Open Build Service project can be found at www.openbuildservice.org. And the openSUSE project is hosting a public instance of OBS at build.opensuse.org which is not limited to SUSE distributions.