Try and track down a few guild mates that might still be playing. Short of that look for a guild to join and they can probably get you going again fairly quick. Best bet either way is jump in, start playing and ask questions as you go.

If you haven't played in several years, here's some of the big changes:

1. One Tamriel - Veteran Ranks have been removed. Leveled zones and quests have also been removed. Now your character is battle-leveled to Cp 160 (just like the old battle-leveling for Cyrodiil to Vet 14). You can go anywhere in Tamriel, do any quest at any level, and you won't ever out-level enemies and zones the way we used to. Craglorn is also now a solo-capable zone, though there are still group quests there. You can now group effectively with players of any alliance (outside of Cyrodiil) and any level.

2. Level Up Advisor and Skill Advisor. As of this latest patch, ZOS introduced these advisors to help new players learn about the game and create different builds. You can choose a build to follow or turn off the advisors.

3. Group Dungeons now unlock progressively by difficult instead of by faction zone.

4. Combat: Morrowind made heavy attacks very important to sustaining resources in battle. Horns of the Reach rebalanced gear traits and changed Prosperous to Invigorating (its still useless, lol). There's been lots of changes to class abilities, so just expect that.

5. Warden Class - Morrowind added the Warden class to the game.

6. Transmutation: Clockwork City introduce the Transmutation system to allow players to change gear to a desired trait. It takes 50 transmute crystals acquired through PVP or PVE activities to change the trait of an item to a trait you have researched.

7.Outfit System: Every character is given a free outfit slot which you can use at an outfit station (replaced the old dye station) to effectively create your own costume and dye your weapons. Using styles and dyes will cost gold or outfit tokens to create your outfit. Use the No Outfit selection from the drop down menu to freely dye your equipped gear.

8. Homestead introduced Player Housing. Housing is largely cosmetic, but you can buy certain amenities like crafting stations, attunable crafting stations that match overland crafted sets, training dummies that get you a DPS counter, and transmutation stations. You can also buy storage chests after the latest Dragonbones DLC update.

I'm sure there's more, but those are the big ones I thought of now.