At the Dream Suite, you can visit other people's towns without making any permanent changes to them. You can also upload a dream version of your own town for other people to visit. When you do this, you get a Dream Code that you can share with others so they can see what your town is like without either of you needing to open the gate. This page explains how the Dream Suite works.
After you been mayor for seven days, go to the town hall. If Isabelle is sleeping, talk to her. This unlocks the Dream Suite in the list of public works that you can build.
There is a couch near the back wall of the Dream Suite. Lie down in this couch to upload your dream town for the first time. Luna will ask if you want to share your custom designs or not. After your town is uploaded, your ID card will show your Dream Code. Other players can visit their own Dream Suite and enter your Dream Code to visit your Dream Town.
You can lie down on the couch to update your Dream Town data. When you do, you can change whether you share your custom designs or not. After you update your data, you receive a payment of 5000 bells. You can do this once a day. The payment goes to the first player in your town who updates the Dream Town data for the day.
If you lie down on the bed in the Dream Suite, you can visit other Dream Towns. You can visit a random town, visit a town by entering a specific Dream Code, or search for a town based on player name, town name, or geographic region.
When visiting a Dream Town, you won't affect the actual player's town, so you can do whatever you want in the town (trample flowers, cut down trees, take money, etc.) and it won't cause any problems for the player.
If the Dream Town's player has decided to share his or her custom designs, you will find Wendel the Walrus walking around the town. Talk to him to receive one of the player's custom designs. You will have to overwrite one of your own designs to receive one from Wendel.
You can't take any items back with you from the Dream Town except for custom designs.
While in the Dream Town, you can go into player houses and villager houses, as well as the train station. However, the train tracks are always blocked, so you can never go north and visit the Main Street shops (Able Sisters, Nooklings', etc.) while you are in a Dream Town. In addition, you can't enter a Dream Town's Re-Tail store, Town Hall, or Roost Café.
If you are in a Dream Town and don't know the Dream Code for the town, just read the bulletin board next to the train station to see the town's Dream Code. Write it down somewhere and you can visit it again later. The official Nintendo Dream Town Code is 0000-0100-0017. To find other Dream Town Codes, check out my Dream Code List.