Hi @akhmerov,
As discussed on this forum, gitlab.mattermost.com is intended to be a test server for pre-released versions of Mattermost.
While we've thought about providing a hosting server some day, right now it's a test server and team creation is only enabled during monthly test periods, when pre-released versions are loaded.
There's a wide range of install guides to self-host Mattermost available for you to set up something similar on your own servers, and providers like Rose Host who are offering manage Mattermost instances.
Thanks for reporting broken links, they're fixed now.