Welcome back!
Kerrosh gave a good answer. I’ll add some things.
Chromie Time is available only to characters in the levels 10-49. It is intended to give people a choice of where to level, but 50s can’t level any more, so it doesn’t apply to them.
We are in the limbo between expansions, the prepatch. Shadowlands will launch in three and a half weeks. Then you will have a very clear direction.
Meantime, you are getting the usual overload of information and things to do of BfA as if it were a new expansion, while it’s actually over.
Blizzard will be adding a prepatch storyline, probably starting Wednesday, with quests for you to do to get better gear and see the story that leads into Shadowlands.
You have made a great choice of Argent Dawn as your realm for Alliance.
For the rest of the prepatch, there are three basic things you could choose to follow:
- Make a new character at level 1, and level it through the world.
This has the advantage of introducing you to some of the basics in travel, trade, abilities, geography at a slower pace, and you can choose a second class and see how other classes work. Eventualy, all of us who stay do make other characters called “alts” to see the game in more than one way.
- Start on the BfA quests.
You can open up BfA, get a little gear and a little gold, learn the Flight Points, and see some of the story.
- Go exploring in lower expansions on your Druid
While level 50s are not eligible for Chromie Time, they can go everywhere at any time. You can do quests from any expansion. You can walk in and solo dungeons and raids from previous expansions - earning mounts and pets from drops there while you’re at it. You can earn Achievements, of which there are thousands.
In the circular mimimap top right of your screen, there is a magnifying glass icon. Click on that and tick “Trivial Quests” on. If you are exploring older expansions that means that quests thatare too trivial for a mighty level 50 will still be shown. 
P.S. You should bookmark the websites
wowhead.com for quests, maps and items and
icy-veins.com for all about how to play your class
They will come in very handy.
Enjoy!
Please ask again if you have any more questions!