A Little Heavy Reading...
At this point, you're progressing through the main story, and finding numerous different types of item with various modifiers. If you're not playing one of the Guided Builds, you're also exploring the Passive Tree and all the different effects available on it.
Trying to describe all the possible modifiers and effects here would be an information overload. However, I can't predict what mechanics you'll be finding as you go. To that end, I've included a separate section to describe basic mechanics, and I'd encourage you to refer to it if you want a primer on certain mechanics. Nothing in the Mechanics Reference assumes any knowledge that has not been introduced by this point, so you could browse them all if you wanted - but there's a lot of information and it's pretty technical, so do so at your own risk.