The further away you move from the equator, the colder/lower the average temperature becomes
The reason this happens is because the sun's rays hit the equator directly. It also has less atmosphere for the rays to travel through and is a shorter distance for the rays to travel
The North and South poles get oblique rays, the sun's energy is spread out because it gets hit at an angle. There is also more atmosphere to travel through (heat is lost) and it's a longer distance for the rays to travel