Tutorial:How to make a spaceship with an interior living space
This tutorial will explain how to make a vehicle that your Kerbals can joyfully run around in.
Now, first thing you need is a cockpit. For this tutorial, I am making a large spacecraft, and am therefore using a combination of Mk3 and Mk2 cockpits. Next, you should have a transfer area. Again, I will be using Mk2 and Mk3 passenger modules.