The MGRS Tools is a plugin for QGIS that enables the users to work with the Military Grid Reference System (MGRS) coordinates in QGIS.
the plugin is documented here.
This repository uses external repositories as submodules. Therefore in order to include the external repositories during cloning you should use the --recursive option:
git clone --recursive http://github.com/boundlessgeo/qgis-mgrs-tools-plugin.git
Also, to update the submodules whenever there are changes in the remote repositories one should do:
git submodule update --remote