For a very good explanation in English of what you see in the photos go to:
http://www.berlinerdom.de/component/option,com_frontpage/Itemid,154/lang,en/
The history of the Dom and its previous buildings on that site may surprise you.
Not all the items on that website are as detailed as the organ, which lists all the stops for the pipe organ. You may even download a sample of music as played there by the Dom Organist Prof. Dr. Andreas Sieling.
If you intend a personal visit:
You must check your backpacks in a locker, when available, €1 thank you.
There are both guided and unguided tours. There are about 8 stages in the unguided tour from the caskets of Hohenzollern royalty in the basement crypt to the walk around the outside base of the dome.
Be prepared to climb stairs for a great view of the Nave below and a walk around the outside for Berlin. The elevator is for handicapped people.
Check time for English speaking tour if you need details.