How to Measure the Aperture of Your Lens

Aperture is a diameter of entrance people but i never knew that so before that i thought it's your aperture versus the f-numbers your aperture and so i looked at the formula it's focal length divided by that f number that's your aperture. So if you have a 50 millimeter lens i don't know the sky so you have a50 f2 or you yeah so a 50 f2 let's say right i don'tknow if that's even a thing but let's say that it is okay that's 50 millimeters at f2 would be divided by two is 25 millimeters that's the diameter of your entrance pupil and your entrance pupil is what your aperture looks like when