You have to get into the room on the right. Climb the poll, and get through the openming.
Once in the room, place the two weights on the door activation switch.
Once the door has openend, throw the rocks out the door, one by one, using Caps Lock.
You have enough time to jump out the door afterwards.
Place the rocks on one of the switches.
Get Lara on the corner of the other, so she can be in a position to grapple the ring.
Grapple and pull!
Go in.A cinematic will play.
You have to find another way out.
Get in the other room that was empty earlier. A rock has fallen, and you can use it to climb out the openning.
In the next room, climb the first pole.
Use the platform to get on the pillar on the other side.
Jump on it, and then on the other one.
Get on the platform in front of Lara, and then on the pillar.
Hop aling to the end of the room.
In the next room, grapple, the ring.
Adjust your height so that when you swing you are level with the ledge.
Swing, and jump. Lara will grab onto the ledge.
You'll have to retrace your steps back to the boat. Go the way you came, and you should be fine. The images speak clearly.