Hiccup and Toothless can search for dragon eggs on the islands around Berk. To send them out to explore, tap the "Search" button above Toothless' roost (left of your Meade Hall), then choose the Dragon you want to find. Note that some of these are limited time, and will rotate out once their time is up. You can choose if you want to explore with one, two or three bags. The more bags you take with you the higher are your chances to find what you are looking for.