Exit the elevator. Follow the path. When Shepard reaches the fountain area, some Geth Troopers will attack. Kill them.
After the combat follow the path. There will be more Geth in the courtyard area. Kill these as well. Climb the stairs.
Near the top of stairs cut scene will begin. After cut scene will be a conversation with Saren.
After the conversation, go to the console. A cut scene will begin and Joker will contact Shepard. After the conversation will be a cut scene of a party member checking if Saren is alive. After another bullet to the head Saren will change into a Geth Sapper like enemy. So this battle will be a bit tough. Just shoot him as he jumps around. When he reaches half his life a cut scene will begin. After the cut scene Saren's shields should be near max again. Just continue shooting him.
A cut scene will begin showing the Alliance Ships attacking Sovereign. After that another cut scene will show rescue squad finding the party. After the cut scene a conversation with the council will begin. They will say the Alliance will be asked to join the Council. Pick whoever you like. The conversation ends with Shepard say he'll stop the coming Reavers. End of game.