If you hold the ball pointing straight out in front of you lengths ways and kick it, it will go end over end. Now if you hold the ball sideways and kick it, more often than not you'll hit slightly off centre, one side or the other, and the ball won't go straight, it'll 'banana' to one side.
If you make it look like you're going to kick to your left, then kick the ball more to the left side of the centre of the ball, it will instead go out to the right.
There are many variations in how you hold the ball as to exactly what the reaction will be when you kick it, this is where a bit of practise will help
For example, the same theory works with grubber kicks, you can deliberately 'banana' the ball along the ground too...
Any questions, feel free to fire away.