Much like in real life, money is the fuel that keeps the world of Animal Crossing chugging. Bells are the main form of currency in Animal Crossing: New Horizons on Nintendo Switch, and there are a variety of ways to earn them. Once you have enough Bells in your wallet, you'll be able to buy clothes and decorations for your villager, but the more practical use for your Bells are payments towards your home.
Exchange Nook Miles for Bell Vouchers
During your playtime with New Horizons, you'll be earning Nook Miles for doing various and assorted in-game tasks. These have no monetary value by themselves, but you can take these Nook Miles to the Nook Stop machine in Resident Services.
On the bottom right corner of Resident Services is a terminal. Within the terminal menu, you can redeem your Nook Miles for a number of rewards, one such being a Bell Voucher. You can buy as many of these Bell Vouchers as you can for 500 Nook Miles each. Take them to the Nook's Cranny store to exchange them for Bells. one Bell Voucher will earn you 3,000 Bells.
Selling Items in Animal Crossing
There is plenty to buy from Timmy and Tommy Nook in the Nook's Cranny general store, but you can sell nearly anything you own to these two for Bells. To maximize this, ask Timmy or Tommy what the Hot Item of the day is. Whatever item it is, it will certainly be something you can craft. These items will sell for more Bells than they usually do, so craft as many of these items as you can and sell them before the store closes at the end of the day.
You will likely catch a variety of fish and bugs on your island; some of these creatures are of high value at Nook's Cranny no matter what the day is, such as Tarantulas, Emperor Butterflies, or big fish such as Sturgeons. You will also dig up fossils around your island, and you can sell fossils that Blathers has assessed in your museum to Nook's Cranny for a hefty price.
A number of visitors and non-playable characters on your island will take certain items as well. For instance, plant and flower vendor Leif will take your weeds and sell them for a higher price than Nook's Cranny. Likewise, C.J. will do the same for fish and Flick for bugs, both buying their respective kinds of items for 50% more than the price that Nook's Cranny offers.
Plant Money Trees
Islands in Animal Crossing are populated with fruit trees, but you can fulfill a fantasy by also planting money trees. Every day on your island, you'll find a gold glowing spot somewhere random on your island. Use your shovel and dig a hole in that spot, and you'll nab a bag of 1,000 Bells. However, this will leave a glowing hole in the ground. This is where you can plant a Bell Tree.
Take any number of Bells from your wallet and bury them in this glowing hole. If you bury an amount of Bells equal to or less than 10,000, you are guaranteed to grow a tree that will drop three times as many Bells. However, after 10,000 Bells, your return will be left to probability. There's a chance that you can bury a much higher amount than 10,000, but more than likely you'll end up growing a tree that will give you three bags of 10,000 Bells each.
Finding Bells on Your Island
Many Animal Crossing players get in the daily habit of hitting rocks and trees around their island, with the chance of mining crafting materials and finding items. Shaking trees may also drop a small number of Bells. However, every day, one out of the many rocks on your island will contain Bells instead of the usual rocks and iron nuggets.
Once you find that rock, hit it with a shovel or ax a total of eight times in quick succession. Doing so will earn you around 20,000 Bells.
The Turnip Market
Every Sunday before noon, a traveling vendor named Daisy Mae will be selling Turnips. These prices will vary over time, and their selling price at Nook's Cranny will similarly fluctuate through the week. This is essentially the stock market of New Horizons, and waiting until the right opportunity when the value of turnips is as high as it can be can net you a large number of Bells. Check with your friends to see what the turnip prices are on their islands.
What to Use Bells For
Bells are used to buy various goods all over Animal Crossing: New Horizons. Along with items in Nook's Cranny, you can buy clothes at the Able Sisters store. Traveling vendors will also stop by your island and sell their wares.
More importantly, you can use Bells to pay off your home mortgage through the terminal in Resident Services. You can also talk to Tom Nook and spend Bells on upgrades to your home and adding infrastructure to your island, such as bridges and inclines.