You need to know other player's unique tag to add them to your friend list. (This tag is totally different than the name you choose for your camp, way shorter, and it cannot be modified). Once you have the player on your list, you'll be able to send a gift once a day, and visit their camp. After that, the gifts you receive from your friends will contain egg fragments, which will help you get more eggs, in order to have more Friend Dragons! And if you are lucky, you will get some eggs in a gift too!