For F-stops, the biggest hinderance to understanding is the somewhat obscure appearance of the numbering scale -- kinda like learning tennis without knowing that the scoring system was (apparently) derived from using the minutes-hand of an old fashioned clock for keeping track of the score (15 .. 30 .. 40 .. etc..).

With F-stops, the sequence is: 1, 1.4, 2.0, 2.8, 4, 5.6, 8, 11, 16, 22, ..

Which just happen to the be the (approximate) square-roots of successive powers of two, in hommage to the inverse-square rule for how light spreads out over distance.

[EDIT]
Oh, and the actual F-stop numbers are actually fractions (or ratios), with the above numbers on the bottom. So 1:1, 1:1.4, etc.. or 1/1, 1/1.4, etc..

So the biggest F-stop (widest lens opening) is f1, or 1:1 or 1/1. Near the other end of the scale is f22 (tiny pinhole of a lens opening), which is short for 1:22 or 1/22, which lets in only 1/512th the amount of light as f1 does (22 is approximately the square root of 512).
[/EDIT]

Cheers