The main button bar has five predefined buttons, quit (which causes the application to quit), run, which calls the simulate procedure, and stop which sets the running flag to zero, suspending the experiment. Command calls the command line interpreter, allowing you to interact directly with the TCL interpreter. Object Browser is a widget allowing you to graphically drill down into the objects defined in the model.
Additionally, there are two user defined buttons, which can have functions bound to them by adding TCL code after the GUI command like the following example:
GUI .user1 configure -text condense -command condense