This shares one of the meanings you learned for the kanji: after. You can differentiate this one from 後ろ (which you may or may not have seen yet) thanks to the で on the end. Some people believe that after something's dead (で), it goes to an afterlife.
Since this word consists of a kanji with hiragana attached, you can bet that it will use the kun'yomi reading. You didn't learn that reading with this kanji, so here's a mnemonic to help you:
After. Everything happens after. It's a cause and effect chain. One thing happens, and then another thing happens after. This is life. This is the universe. Everything is after. It's an automatic (あと) cycle that just keeps going and going and going.
to watch later
to say later
to do later
Please come to the hotel later.
I will email about the meeting later.
I will watch TV later.