You can unlock the dream options by acquiring the Luna bed. Once you obtain the bed the game grants you access to the dreamworld. After the option is unlocked, you do not need the Luna bed to dream, any bed that allows you to lay down inside your own home will show the dream options.
To Upload a New Dream
Lay down in a bed inside your own home.
The game will ask you, "Should I get some sleep?"
Press the "A" button on your Switch
Luna, the lady who runs the realm of dreams, will appear.
Choose, "About my island's dream..."
Choose, "Update the dream"
Luna will connect you to the internet and confirm that you wish to update your dream.
After uploading a dream Luna will mail you a ticket called a “Dream Bell Exchange Ticket”. Timmy and Tommy, the twin raccoons who own Nooks Cranny, the general store, will happily buy your ticket from you for 5,000 bells.
The game will assign you your own personal dream address that you can share with others. After uploading your first dream, the address will appear in your passport.
You can upload a new dream once per day. Not bad for some basicly free cash.