Where do I have to search for a specific Pokémon?
Solution 1:
The first picture means that you find the Pokemon by walking around in that area. In outdoors areas, this means tall grass. Indoors, it means just walking around (like in a cave).
The second picture indicates whether or not you can find the Pokemon via surfing.
The third picture indicates whether or not you can find the Pokemon via fishing.
Solution 2:
The three images represent respectively walking, surfing, and fishing.