How to find Discount Rate in NPV

[Dale Viljoen]

I have been watching coutless videos as well as articles about NPV and I am starting to wrap my head around the concept and what it is used for. Now from what I remember the equation goes as follows, Cash Flow / (1+ Discount Rate) ^ Time. In the videos I have watched they just chose a random percentage without explaining it in a way I understand. Help on this will be very well appreciated!