Contact at highest point at which you can stretch upwards (or lift yourself upwards if you are not me) of the ball on the way down from the toss, and making contact with the upper half of the strings. How much above the contact point is the apex of the ball toss? 1 foot.
How far: traditional instruction: 1 or more feet into the court so that you are angled forward on the first serve, 1 o'clock position. For second serve, right above or even behind your head (12 or 11 o'clock).
Modern tennis: J shaped toss on the first serve to about 12 o'clock.
This is just one opinion.