Decals, unique paints, mainly are for camouflage, as for other details, like @F104Deathtrap explained are related to sone functions, and for example, like most people like to add a really small lines on their wings, which means that is the detail which represent the connections or attacments for the wings, part by part... Also like nuts, screws, lights, etc ;-)

Hmmm. The cool thing about planes (as opposed to cars) is that most of the stuff is there because it needs to be there. All the weird littles bits and bumps and details are equipment that serves a function. To make it look right, it helps to learn about what it does and why it's needed. But that takes a long time to figure out. If you want, I can put together a short list of things often found on the exterior of a combat jet.

@AviownCorp ah, there are seams, chassis niche, more detalied engine and other stuff

@getorge I mean I want to know why those are used in a real plane.

@AviownCorp it is just a decoration, that helps to enjoy this palne

@getorge thank you for your support! But I don't know the meaning of those details

try to get inspiration by this

@AviownCorp Like this

@RailfanEthan please give me some examples

Try adding warning labels, which could be as easy as putting in a 0.75x0.375x0.1 fuselage in the wings