The first method for adding cues is the Toolbar, which is this handy dandy set of icons right here. To add a new cue, simply press the icon to add it after the selected cue.
Or you can simply drag and drop.
When dragging and dropping, note the blue bar with the ball at the side. This will tell you the placement of the cue being dropped; whether that’s before / after a certain cue or if it will be dropped inside out outside a group of cues.