No specific command format. In SCS Editor select 'Add Audio File Cue'. In the blue Sub-Cue area second line browse for the required audio file (...), trim the Start and End points as required, enter Fade In and Fade Out times (my default is 0.200 secs in, 0.500 secs out), to avoid possible clicks at the beginning of the track and an abrupt ending. Leave 'Activation' in the green area as 'Manual' (with space bar). Repeat for tracks 2 and 3, but for track 3 set 'Activation' as 'Auto Start' (from dropdown) '0.0 seconds' 'after end of cue' 'Previous Cue'. For the latter you can also enter a specific cue if required. When SCS gets to the end of track 2, track 3 will auto start. Depending on the tracks, if you want achieve a seamless transition you could change it to '0.5 seconds' 'before end of cue', for example, or longer, and adjust the Fade Out of track 2 and Fade In of track 3 to suit.
The resultant cue list is usually worked through in a linear fashion using the space bar. To take tracks out of order you can navigate the cue list with up/down arrows or the mouse. Alternatively, to play tracks completely randomly you could set the Activation for each cue as 'Hotkey (Trigger)' and allocate a specific key to each track. A single keypress will then play that track.
HTH