As others have said, ground speed =in flight= is simple 9th grade algebra. Distance ÷ time = rate (your car speed is calculated in "miles-per-hour", right?. That's just distance/time)

The E6B front side wheel is a ratio calculator. It talks in of "this" ÷ "that". So take the distance ÷ time and put it right on the E6B: distance over time and the pointer will give you your ground speed.

You use the wind side of the E6B to calculate =expected= ground speed based on =forecast= winds aloft.