You ask a lot of questions here, and the answer to just about every one is, "it depends." I'm going to stick to the abstract here, but maybe someone else could give more specific examples.

Feudalism as a concept seems simple on paper. Peasants work a patch of land in exchange for protection from their feudal lord. That lord is subject to someone above him, who is subject to someone above him, et cetera et cetera. Each spot on the ladder has a feudal obligation to protect those below them and to serve those above them. This is the conventional wisdom, anyway.

The Song of Roland is the go-to primary source that describes the ideal feudal relationship. It's an 11th century epic poem about feudal lords setting aside their personal wants and needs in favor of following the feudal system. It's the bane of every student who's ever taken an "Intro to Medieval History" course and a terribly dry read, but you can find the translated text everywhere online.

The problem is that feudalism is a very general term. It has to be. There is so much variability and nuance, from place to place, culture to culture, religion to religion, and time to time.

Since the 1970s, there has been a camp in the middle ages and medieval history fields to do away with the term "Feudalism," because of how much variability can exist between feudal societies. They'll tell you that it's such a general term that it doesn't really tell you anything meaningful about the society.

Elizabeth A. R. Brown was the first to argue this idea, and reading her article "The Tyranny of a Construct" might give you a good idea of what the traditional system of Feudalism looked like on paper, and how inaccurate it can be.

This is not a settled debate by any means, and there are plenty of medieval historians who will tell you that feudal societies had more than enough in common to justify using the term feudalism to group them together.

If you are looking for more specific information, I'd suggest narrowing down your search to a specific region.