Fruit trees are an essential mechanic in Animal Crossing: New Horizons that you want to become familiar with pretty quickly. You begin the game with some fruit on your starting island, but there are others you can grow.
Whenever you have a new or old fruit in your inventory, you have the option of selling it, eating it, planting it to make more trees on your island. Before you can grow one of these trees, you do need to have access to a shovel. You can obtain one from Blathers when they arrive at your islands to help host the museum. Once the museum opens up, he gives you the recipe, which you can freely use moving forward.
Now, find a location you want to plant your new fruit tree. Once you find your ideal location, take your shovel out and dig a hole. For the next step, go into your inventory and select the fruit you want to plant at that location. You want to continue holding the shovel for this part. With your shovel in hand, you will planet the fruit tree, and you need to water and take care of it to have it grow.
Growing things in Animal Crossing is a timely process, so you need to have a little patience through this process. Don’t get too carried away because there’s plenty of things to do on your island, but make sure to water it every so often so it will grow faster.