Ubuntu MATE homepage: https://ubuntu-mate.org/
If you want to see the Official Ubuntu HomePage, use this link: Official Ubuntu HomePage
If you would like to visit Ubuntu Web Forums, here's the link: Ubuntu Web Forums
For the Official Ubuntu Wiki, here's the link: Official Ubuntu Wiki Front Page
Click on 'Official documentation', and choose an appropriate link to download from there.
Also be sure to look through Community documentation and add some of those links to your Firefox Bookmarks.