Hi Bittercup, welcome back to Azeroth! :)
Cataclysm was released nearly 8 years ago now, and by the looks of things you last played regularly back in 2011 which is 7 years ago (and nearly 4 expansions!). You're absolutely correct in pointing out that an online game like World of Warcraft can change a lot in that time.
Although some abilities have been removed, a lot of the old classics are still there. If you press N (assuming you're using the default keybindings) to open the talent pane, when you select a Talent Specialisation it will show you the 6 abilities that generally form the core gameplay of that class. By reading the tooltips of those abilities you can generally work out the basics of how things piece together combined with which talents you choose.
There are still training dummies in capital cities which you can wail on for a bit to figure out the finer points. Once that muscle memory kicks back in, you might see it have a positive effect on your DPS.
Gear wise, level 110 is currently the max-level. A lot catch-up systems were introduced in previous expansions to ease the leveling curve, so gear that was the Crème de la Crème several years ago, simply isn't anymore. As Calydor mentioned, you'll quickly replace your former raid gear on the way to 110.
You can also create a level 100 Trial character. From your character list, click Create New Character and then select Class Trial at the top of the screen. This will give you a temporary character at level 100 with a short tutorial on the basic combat rotation of one of the talent specializations of that class. It's handy if you want to get a basic feel for how something plays.
Our
Returning Players Guide has a high level overview of the major game changes. Also, as Tèsla pointed to, there are a wealth of community created resources out there that dive much deeper, and can provide advice on talent builds, stat weights etc.
The
New & Returning Players Questions & Guides subforum is also a great resource.
Of course, we appreciate that coming back to the game after so long can be a pretty daunting experience, and we're always interested in hearing what the pain points are and what returning players feel could be improved. We welcome any such feedback but we'd ask that it's expressed in a calm and constructive manner.
