"You... Well, you've been dead a long time, so you're going to see a lot of things you won't understand."

Hey everybody, long time no see! In fact, a lot of you probably don't even recognize my username. I haven't been around since about the time that the first DLC dropped, and I didn't post too much even before that. A few people might recognize me from when we first started doing the Vault of Glass, and I still have some of you on my friend list. Essentially, here's what happened: college can take a lot of time. Over the past year, I've been finishing up my undergraduate studies (among other things), which basically took away my time to really delve into Destiny like I would have wanted to, so I stepped away from the game for a while. That sort of thing just happens when you take on as many responsibilities as I chose to. I double majored and had two part time jobs plus an internship that was basically another part time job, but giving up my Destiny time to focus on those things paid off. Recently, I successfully graduated with the highest GPA in my graduating class at a 4.0 and am now down to just one part time job while I get ready to move to Japan to teach English (I chuckled to myself when I saw the post from LordOwen saying that he had just done that). As a result, I have a lot more free time. So, now with the release of House of Wolves, I'm starting to try to get back into the game.
Here's where I ask for help. It seems like Destiny has changed a lot since I last played. Any advice from you fine folks here would be much appreciated so that I can get back into the game quickly. To put it in perspective, I've never played Crota's End (but would love to go through it with some of you if that gets set up at some point soon), and I have no idea about any new mechanic that wasn't in the original base game. My Warlock is level 28, so I'm still not too far back from the new end game from what I can tell, but I do know that what little I've played so far tells me I have a lot to learn. So, my fellow guardians, please teach me the new ways of the Light, either here or by hitting me up in game. I'm on Xbox One, GT: DerekT07. Thanks so much for the help in advance!

tl;dr I don't understand what's going on because I haven't played in a while, so please help!