When you first move into your village, there will only be a few shops open. You can upgrade and add some new shops if you know how to unlock them.
You can upgrade the item shop so it sells more items. You do so by spending bells at the item shop and doing a few other things. Only items that can be "sold out" count toward your total. In other words, stationery, wrapping paper, and melody cards don't count toward the bell total. Fortune cookies are counted as 500 bells.
Upgrade to the Convenience Store (T&T Mart)
To upgrade to the convenience store (T&T Mart), you must have a house rather than a tent. Upgrade from the tent by giving 10,000 bells to Tom Nook. The convenience store upgrade occurs after 12,000 bells have been spent in the shop (all players on the game card can contribute) or you have bought at least 15 items. It must be at least 10 days since you created the town.
Upgrade to the Supermarket (Super T&T)
The supermarket is called Super T&T. The supermarket upgrade occurs after you have spent 25,000 bells in the shop. It must be at least 10 days since the convenience store opened. It must be at least 10 days since the garden center opened.
Upgrade to the Home Center (T.I.Y)
The upgrade to the home center (T.I.Y) occurs after you have spent 50,000 bells in the shop. It must be at least 21 days since you built the supermarket.
Upgrade to the Department Store (T&T Emporium)
The upgrade to the department store (T&T Emporium) occurs after you have spent 100,000 bells in the shop. It must be at least 30 days since you built the home center. You also have to pass Gracie's fashion check at least four times before the emporium will open.
To unlock the garden center, the total number of times you have done any of the following actions must be at least 30: pulled weeds, watered flowers, planted trees or flowers. If you don't have a watering can and haven't earned 100% approval rating (see the starting the game guide for information about increasing your approval rating), talk to Isabelle at her front desk in the town hall and ask for advice. If you do all of the things she asks, she will eventually give you a watering can. Use it to water flowers, which counts toward unlocking the garden center. (As a side note, you can also get a free fishing rod or bug net if you keep asking Isabelle for advice before you achieve a 100% approval rating.)
Nook's Homes is open from the beginning. After you pay off your down payment and get a house instead of a tent, Nook's Homes will start selling exteriors, such as new roofs, mailboxes, and so on.
Happy Home Academy
After you pay off your first home loan using the ABD in the post office, talk to Tom Nook. Then exit Nook's Homes and go back in. Tom Nook will introduce Lyle, who will give you advice about increasing your HHA score.
Happy Home Showcase
If you're still living in a tent, pay off your down payment by giving 10,000 bells to Tom Nook. Then use the ABD in the post office to pay off your first house loan. Be sure to talk to Tom Nook after that. The Happy Home Showcase will open the next day.
Donate at least 20 items to the museum, with at least one from each category (bugs, fish/deep sea fish, fossils, works of art). Catch bugs with a bug net, catch fish with a fishing rod, and dig up fossils with a shovel. These tools are available from the Nooklings' Shop. Works of art can be purchased from Crazy Redd.
After you have donated enough items, talk to Blathers each day. One day, he will be thinking about something. Talk to him and he will talk about the museum shop. After that, the museum shop will be added to the list of things that you can build in your town. Just sit in your mayor chair in the back of the Town Hall and ask to build something, then choose the museum shop.
In the Able Sisters' shop, you can unlock a QR code machine that creates a QR code that represents a custom design. Other players can then scan this code to import your custom designs into their games. To unlock this, talk to Sable, who is working at the sewing machine. You have to talk to her each day for several days in a row. Then the QR code machine will be unlocked.
For Club LOL to open, your shop has to be upgraded to the convenience store, and you have to have reached 100% approval rating according to Isabelle (see the starting the game guide for information about increasing your approval rating). Then the next day that you play, Dr. Shrunk will be outside of your house and will ask you to get signatures for his petition. Agree to do so, then talk to six of your villagers and ask them to sign the petition. Once you have six signatures, go talk to Dr. Shrunk in Main Street to give him the petition. Within the next four to eight days, Club LOL will open.
Spend at least 8000 bells in the Able Sisters' shop to unlock the shoe store, which is called Kicks. It must be at least ten days since the town was created.
To unlock Shampoodle, spend at least 10,000 bells in Able Sisters' or Kicks. It must be at least 10 days since Kicks was built.
Fortune Teller Shop
Katrina is the fortune-telling cat who sometimes shows up in your town square. To unlock the fortune teller shop, you or any other residents of your town need to have Katrina tell your fortune 20 times. You can even go to other towns and visit Katrina there. This may count toward unlocking Katrina's shop in your town.
After the 20th fortune that she tells you (or anyone from your town), she will stop you when you try to leave and will suggest building a public works project for her. The mayor of your town can then sit in the mayor chair in your town hall and choose the Fortune Teller's Shop from the list of public works projects. Lloid, the fundraising gyroid, will be in the train station to collect donations for the fortune teller shop. After you have donated enough Bells to Lloid, the Fortune Teller shop will open the next day.
The Dream Suite is a place where you can visit dream versions of towns, where you can do whatever you want without affecting the real town. 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. Just sit in your mayor chair in the Town Hall and ask to build the Dream Suite.
The Roost Café
Donate at least 50 items to the museum, and open the museum shop (see above). After the museum shop has been open seven days, talk to Blathers. He will eventually be thinking about something when you go into the museum. Talk to him at that time to add the Roost Café to the list of public works projects. Just sit in your mayor chair in the Town Hall and ask to build the Café.