The top-spin or 'kick' serve is created by the racket face brushing up the back of the ball.
It creates a serve that loops higher over the net and then dips down into the court.
It can be a very deceptive serve as the ball will swing from right to left in the air (for a right hander) but as it bounces the spin will bite into the court and it will kick high and to the right.
This makes it ideal as a second serve as the looped flight path makes it safe yet the kick on the bounce forces the receiver back and usually on their weaker backhand return.
To hit the kick serve you have to have the correct chopper grip.
If you nudge it a bit further around the grip to a slight backhand grip then you can generate even more spin on the ball.
Bring the ball placement back slightly and to the left (right if you are left handed), almost as if you were trying to land the ball on your head.
As you go to hit the ball, arch your back more.
Hold your sideways turn longer and accelerate the racket head up the back of the ball.
Your swing path should be more in line with the baseline rather than forwards into the court.
Do not worry where they go to begin with.
Look to create the loopy trajectory and develop it from there.