From the Super Mario Wiki
Directional Blocks are objects that appear in Super Mario 3D Land. They are purple-colored blocks with an arrow insignia printed on their sides. When a player hits one from below, it will move in the direction it points to for a distance that is roughly half of its height/width, which usually allows them to access certain blocks or collectibles they couldn't with a normal jump. Their positions can only be reset by replaying the levels they appear in.