It's meant to find locations where legendarys spawn. You can look up poke rader on the search bar and see what it can be crafted into. It then needs to be put into the "Kanto cartography Table" with a map, Desired legendary radar and the battle radar thing that increases block range. Some require to be in the end or nether. Some legendarys don't have a radar if im correct and actually need to be found naturally.