You are brand new in the GNU/Linux world, aren't you? Welcome. :-)
Try to forget the painful way you used to install software on Windows
(searching the application on the Web, downloading an installer, searching
the installer, executing it, clicking "Next" a dozen of times, removing the
useless entries in the menu, etc.).
Trisquel has a repository of free software that makes it very easy to install
an application:
Run the "Add/Remove applications" (to be found in the main menu);
Type the name of application you want (both Clementine and Mumble are present
in Trisquel's repositories);
Check the boxes in front of them;
Click on "Apply changes";
Enter your password when queried (the user needs to be allowed to perform an
administrative task).
A few minutes later the requested applications are ready to be used. :-)
