What JN99 said. Say you want to play "I'm Tore Down" following the Clapton arrangement: there are at least two downloadable versions on the user forum.
That song:
- starts on the turnaround
- has breaks on the I in the first verse
- has a "long I" (8 bars of one instead of 4) with breaks in the second verse
- has regular verses for a while and solos
- goes back to the long I after solos
- has a breaks on the ending
you will need to have multiple parts in the song and trigger them at the right time. Not everyone took the same approach on the versions downloadable on the forums. One of them for example decided to have an intro with the turnaround and the 1st verse, then a repeating "main loop" with the regular verse for solos (useful if you don;t know how many progressions you;re going to take), then the ending is the last long I and the outro. That makes it "easy" to follow: click to start the intro, into will automatically go into the repeating loop until you are ready to end solos, then double click to get into the last verse+ outro. you don;t have to click perfectly on the beat like with a looper, the pedal will be smart enough to keep the beat as it transitions from one part to the other.
One of the free versions on the forum uses the ability to play a bass line too. It basically means some of the midi codes are assigned to bass notes instead of drums, and you need to load a "drumset" that has the bass notes built in, again several of them available for free. if you have a bass player, load a drumset without the bass notes in it. That way I can practice at home with the bass, and turn it off with the band. Of course the bass line was in the wrong key, so I had to transpose it using a midi editor (I'm pretty sure I made that version available on the forum). It's not that complicated, but it's not trivial either, free midi editors are not professional quality, and it helps it you learn a little bit about midi.
So for the most benefit, unless you find that someone already made the perfect setup for your song, be prepared to spend time on the computer to get it just like you want it. In a lot of cases you can start with a midi file of the song that has all the instruments, then remove those, then cut paste and repeat in your favorite midi editor.
Of course you can use one of the pre-canned rhythms, click to throw in a fill when you reach the 12th bar, and keep it at that. That doesn;t work for me for "Tore Down", its structure is just too specific to ignore.