Explain why the temperature at the equator is always hot and the temperature at the poles is always cold?
Basically, the first four answers have covered why the equator is generally hot, BUT, that is not always the case! Cayambe is a 19,000 foot tall mountain in Ecuador that lies on the equator and it is snow capped year-round, and not just a little bit of snow either. I know this evades your main intent for asking, but you said “always” and I wanted to point out the exception.
Basically, you have the sun shining directly on the center (ring around the middle) of the earth, or the equator, constantly. Except, during the night time. (When the earth has rotated away from the sun) It’s the total opposite for the poles. They never receive any direct sunlight. Therefore, they’re frigid. Hope this helps.