If everything worked correctly, you should be able to build gtkmm and all of its dependencies from git by executing jhbuild build (or, if you didn't specify gtkmm in the modules variable, with the command jhbuild build gtkmm).

This command will build and install a series of modules and will probably take quite a long time the first time through. After the first time, however, it should go quite a bit faster since it only needs to rebuild files that changed since the last build. Alternatively, after you've built and installed gtkmm the first time, you can rebuild gtkmm by itself (without rebuilding all of its dependencies) with the command jhbuild buildone gtkmm.

After you've installed the git version of gtkmm, you're ready to start using and experimenting with it. In order to use the new version of gtkmm you've just installed, you need to set some environment variables so that your configure script knows where to find the new libraries. Fortunately, jhbuild offers an easy solution to this problem. Executing the command jhbuild shell will start a new shell with all of the correct environment variables set. Now if you re-configure and build your project just as you usually do, it should link against the newly installed libraries. To return to your previous environment, simply exit the jhbuild shell.

Once you've built your software, you'll need to run your program within the jhbuild environment as well. To do this, you can again use the jhbuild shell command to start a new shell with the jhbuild environment set up. Alternatively, you can execute a one-off command in the jhbuild environment using the following command: jhbuild run command-name. In this case, the command will be run with the correct environment variables set, but will return to your previous environment after the program exits.