The Earth is free falling towards the Moon. Because gravity decays with distance, the near side wants to fall faster than the center, the other side tends to fall slower. So observed on the Earth, the other side "lags behind" and therefore we have high tide there.

The Earth is free falling towards the Moon. Because gravity decays with distance, the side near the moon wants to fall faster than the center of the Earth, while the other side tends to fall slower. So observed on the Earth, the other side "lags behind" and therefore we have high tide there.