The "TclTkGRASS" GUI which allows mouse usage is simply an extension without own GIS functionality. TclTkGRASS offers graphical access to important GRASS modules and makes working with GRASS easier. However, don't forget that it is incomplete and that there are many more modules available than are present in the TclTkGrass menus. Also beware that some modules that are present lack some of their command line options in their tcltkgrass window.
If TclTkGRASS was not started automatically during GRASS startup, you can do so at the GRASS prompt with the command tcltkgrass&.