First, this formula determines a "start date". The "first of month" is calculated with the DAY function here:
Then n * 7 days is added the first of the month, to get a start date n weeks from the first of the month. In the generic form of the formula, n represents "nth".
The next step is to calculate the adjustment required to reach the final result. The adjustment is calculated using WEEKDAY and DAY:
Inside WEEKDAY, the first of the month is again calculated, then 8 days are added and the value for dow (day of week) is subtracted. Day of week is abbreviated "dow" in the generic form of the formula. This is a number between 1 (Sunday) and 7 (Saturday) which can be changed as needed.
Finally the calculated adjustment is subtracted from original start date to get the final result.