You can also have a 4 measure blank intro as Dereka said using the style creator by muting all parts of the intro.
This way the main will start automatically at the 5th bar without having to press any button,
if both hands are ocuppied at playing chords and melody.
To be able to keep the right tempo at a 4 measure empty intro, you could press the metronome button if you want to record it right.
If you want the parts of the style to play but you just don't want the drums of the part,just delete(or mute) the drums of the intro.
The keyboard starts to record when one of these 3 happens:
1)You press the start button.
2)Hitting any key(note) of the keyboard.
Playing some music with no style first and when you hit the sync or start button the style begins too.
If you want to play the melodic part at the begining and want to use all the keys and not LH chords(lets say your both hands play a piano piece) ,
then deactivate the Acc button to the left first.
When you finish the melodic part,activate the Acc button again and press sync start or start.
3)Use the synchro start button.
a...Playing a chord with your left hand and the style begins to play(most common way).
b...Have the synchro start on,play something with your right hand first and when you play a chord with your left hand the style begins(Acc button should be activated)