You select a command, a single element appears on a line that looks like this:
You then right-click on the command element and select an available command from the right-click list. Once a command is selected from the available menu, the elements associated with that command will appear on the line based on the script syntax for that command. While the elements associated with the command can then be entered or selected, should you want to CHANGE the command itself you'd need to delete the command and then re-insert a new blank command (and then re-select from the right-click menu).
Once a command has been selected, right-clicking on the command may provide a list of available associated commands which when selected would be inserted before or after the command (Else commands appear after an If, while most all other associated commands appear before the selected command). Associated commands that appear before a command are "linked" and cannot be separated from the command they are added to. Similarly commands that appear after a selected command (the Else that is inserted after an If) is restricted in it's movement, bound between the If and the terminating EndIf although these are permitted to be separated by insertion of intervening commands.