Manual is the place to start from.
The difference between Touch.SpeedAt(n) and Touch.SpeedForID(m) is the index presented by n.
When you touch screen, you can do this with more then 1 finger. The system makes a list of all those touches. An index is a place in a(ny) list. An index always starts at zer0. So, the first item in a list is always zero.
The n in Touch.SpeedAt(n) stands for the nth finger in the touch, or the index of a finger in the list.
The m in Touch.SpeedForID(m) stands for rather a special number.
When using the conditions 'On any touch start' or 'On any touch end' the expression ......
Touch.TouchID assigns a number to 'gesture' of the fingers that are on that moment on screen.
So, say you touch the screen with 1 finger, and a moment later with a second finger .... then ...
On any touch start
___________action ... 'set m to Touch.TouchID' will hold a number, and that will be different on the second touch.
Now you can use m in Touch.SpeedForID(m)