While in the past, Bran hears Meera screaming that they need him to take over Hodor's body so that Hodor can help them all escape. In the past, the Three-Eyed Raven tells Bran to listen to his friend. And then something happens to Hodor. In the present, he gets those all-white warg eyes, and then they revert back to his natural blue. Bran is now controlling him -- but is he doing it in the past or in the present?
This is exactly why I hate time travel. There are just so many questions involved. Like, did this all have to happen just so Hodor could have a seizure back in the day, which is what ruined his mind? If Bran had died when he fell out of that window in Episode 1, would Hodor have snapped out of it and been fine again? Who knows?! Stupid time travel.
Anyway, Meera is telling Hodor to "hold the door," and that is all the gentle giant can hear or say in the past, the two time periods bleeding together, with Bran serving as a conduit between them. We can learn a few things about Bran's powers from this. As we learned at the Tower of Joy, when Ned heard Bran call for him, his actions in the present can certainly affect the past. Is Bran's purpose that he can influence the past, so that he can reshape people's destinies? One thing's for sure: we know that warging through time is hazardous to Hodor's health.