To use, interact with the ABD machine in Resident Services and select 'Invite a Camper'. This will prompt you to hold the Amiibo to the touch point and allows you to get the character to visit your campsite. After 3 visits in which you fulfill their request for you to make them a souvenir, you can ask the villager to move to your island! If your island is already full, the camper will ask you to select someone for them to replace.
Photopia (Harv's Island) is a special island in Animal Crossing: New Horizons where you can use models of the various villagers to create photoshoots. These models are unlocked by using Amiibo cards/coins in Photopia.
Once unlocked, you can dress these models in a variety of clothing, assign them emotions to express, decorate the scene with props and pick out the camera direction before taking your photo.
If you're using a Joy-Con controller or Nintendo Switch Lite, then the NFC touchpoint is located on the right controller stick. If you're using a Pro Controller, however, then the NFC touchpoint is the Nintendo Switch logo in the top-center of the controller.