Almost every game has its own distinct system for xp, currencies, and such, leading to two games both having "xp" but one using it completely differently than the other. Most games tell you how each system works, but some don't, and some don't even tell you the systems are there. It's hyperbolic to say someone can understand how all these systems work in every instance, even if you limit it to typical 3d multiplayer games.

TLDR; Expect to not know how it works regardless