Are you using a keyboard or gamepad ?
Basically, there are two stages to offensive plays. Before the ball comes out the maul/ruck/scrum, you press left/right/up/down on the D pad to select pivot/dummy switch/pocket/classic line ups.
pocket is just a kicking play.
Classic is just a straight forward line up.
With dummy switch/pivot, you need to press and hold the number corresponding to the guy you want the ball to go to. The outside half will run automatically and pass to the selected three-quarter.
When it comes off it's awesome, you can split defences wide open, it' well worth persevering with.
If you're using the keyboard, same principle. I couldn't play with the keyboard myself unless I sprouted 5 more fingers on each hand.