OK, here is how serve works:
Holding "down" will ad a kick to it, holding "down" "up" will add slice.
Start holding the shot button and keep holding through the whole animation, until after the serve is made. You can keep holding "up" or "down" all the time to add the desired spin. The sooner you start holding it the more spin the serve will have. You hold "up" or "down" also all the way through the serve. Or you can choose a rather flat serve without adding spins.
Now for placement. You need to slightly press and hold for a split second the desired direction - "left" or "right". You should do that after the toss, timing varies with each player, but sometime after the toss there is a sweat spot.
Example, for a kick serve: Hold shot button and then press down, wait till the player toss, press and release direction (left-right). Keep holding shot+down until the serve is complete.