Instead of clicking and dragging the square in the lower right corner of the cell, you should try instead to double click it. This will autofill it down.
Also, you should get used to using "ctrl" and "shift". When I use excel I go extremely fast because I use lots of keyboard shortcuts. Let me walk you through an example and let you know exactly what I would type. Lets say you have data in Columns A:E with 20000 rows, and want to create a formula for F. Follow these steps: