Maintenance for the week of April 22:
• [COMPLETE] Xbox: NA and EU megaservers for patch maintenance – April 24, 6:00AM EDT (10:00 UTC) - 12:00PM EDT (16:00 UTC)
• [COMPLETE] PlayStation®: NA and EU megaservers for patch maintenance – April 24, 6:00AM EDT (10:00 UTC) - 12:00PM EDT (16:00 UTC)
Like every other expansion for one year or so following their release, they are a separate thing. You need to buy it, along with the base game, to play it. After about a year or so, they'll be antiquated and turned into "DLC", which means you can buy it with crowns, gift/sell to other players and access it with ESO+.