The GUI provides a way to execute generic scripts. This means that custom-made scripts designed to be ran from the command-line can be accessed from within the GUI.
To prepare to execute a generic script, find the relevant script file in the bottom panel on the left-hand side. View the script by selecting it, right-clicking, and selecting View from the pop-up menu. A well-documented script is likely to provide a synopsis of what it does in the first few lines which should include a description of the expected command-line parameters.
To actually execute the script, right-click on the file and select Execute... from the pop-up menu. This brings up a window giving the opportunity to specify an arbitrary number of arguments. The number and type of text that should be entered here clearly depends on the nature of the script. Selecting Ok creates a tab in the main GUI window and runs the script. The newly created tab summarizes the script launched, records any output produced, and indicates its exit status (running/finished/failed).