I have students that get this a little confused as well so dont feel bad.
I have them hold up a ball straight in front of their eyes as their navel is pointing straight to the net (shoudlers are parallel to the net).
As you face the ball, imagine a click face on it. The clock face is used for not only your swing path but also where you need to strike the ball. So they are used for both. For example, a twist serve will be mainly a swing path you want going from 8 to 2 or 7 to 1 depending on how much twist you want vs topspin.
On a slice serve you want to strike the ball at the 2 o'clock part of the ball.
The clock face combined with your toss for any kind of serve will help you not only generate the right swing path but also help you hit the right spot on the ball.
Now if you toss the ball up high, it does not change where the clock face is, about the only thing that changes is your angle to the clock face which should help you know how to swing or where to hit the ball for the serve your trying to do.
Here is a site to help you with tossing