Space Station V - Help

Hi there
I am a Total Newbie to Blender and i am Modelling Space Station V from 2001 Space Odyssey. I have made the central part of the space station however i am not sure how to make the hanger. I have a cylinder and not sure how to create a box on/in the cylinder so i can bevel it in to create the hangar like below.
The cylinder has faces and i don’t know how to put a box in those faces. Is there a easier way or do i have to start again.
Thanks in Advance.

check out grey beard’s bath tub tutorial

it’s not exactly the shape you are after but the method of creating the hole will work for you

(it’s a big DL but worth it if you’re new)

Not sure why it wasn’t posted the first time but here is a video I made yesterday on my way home:
In the upper left corner you can see the keys being pressed.

Thanks guys for the replies.
Thanks Musk i will try that tonight when i get home, and that was what i was looking for. Much Appricated.
Thanks for the Link waylow those tutorials will be a help.