Hey, I need to compare two .esp.

how do I do that? Is there an easy way to just check the differences? Also, is there an easy way to understand what is inside?

TES4Edit is what you want. You can see exactly what records are in each esp and easily spot conflicts.

Understanding what you're looking at? That's different, but generally the record types aren't too hard to figure out (CELL, NPC, etc).

If you want to see things like landscape or cell edits, the easiest way is to load them both in the construction set (after you've checked for conflicting areas in TES4Edit) and zoom into the area in question.