The lift if for you to gain time and put your opponents under pressure at the rear court. The forehand net lift is played from your forecourt to your opponents rear court.
Start with a split step and time just after your opponents hit the shuttle. A relax forehand grip with the racket head above the hand at the approach. Make a positive lunge with the rear heals slightly raised.
Push the hand forward and supernate the forearm. Create a large angle at the elbow and a small angle at the bend wrist. Tighten the grip on impact hit through the shuttle allowing the racket momentum for the racket to promote through.
Slide in with the non racket foot and sashay in recovery. Try it out and learn from this education badminton video.