That's... an interesting sense of style for the room decor...
Obito wakes up being watched by an ancient Madara with only one Sharingan, and Obito initially thinks Madara is the god of death. Obito thanks Madara for saving him and wants to return to his friends, but Madara states that Obito has to repay him and there is no way to leave the place they are currently in. Madara isn't quite sure how Obito survived being crushed by the rocks, but he managed to save Obito. Obito eventually finds out who Madara is and Madara explains he survives by absorbing chakra from the Mazou. Madara reveals that he had left his own eyes to someone else, and he would take Obito's Sharingan if Obito was going to die. Madara then states the wants to change the world and break the cycle of violence and he wants Obito to help him.
The series is in the process of explaining how Obito survived, why he is aligned with Madara and carrying out this Infinite Tsukuyomi plan. From the sound of things, Obito's Kamui probably activated when he was about to get crushed by the rocks and somehow sent him to the place Madara is currently stuck at. Madara probably already has a plan worked out in his mind, and what's left is to convince Obito to go along with it. It's interested that Madara already entrusted his original eyes with someone else. Obito/Tobi mentioned that Nagato's Rinnegans had belonged to him, so perhaps Nagato's eyes are Madara's? We'll see how this all unfolds, and it might take a couple of chapters of flashbacks to clear everything up.