Where to get it

The best place to get mumble is the official website: https://www.mumble.info or download them directly from the github repo: https://github.com/mumble-voip/mumble/releases

I would not recommend any unofficial sources, since some providers distribute their modified version of mumble, from which it is not sure what they have build into it, this is possible because mumble is open-source.

The download link is straight on the mainpage, chose your operating system and the stable release, download, execute, go through the installer and you are done.