This might be simple but i'm lost.

I created a building that you could walk into with two floors. When i brought it into unity, I can't use the stairs and i just walk through all walls. Someone told me to use Rigid body. But even when i use that, I still run right through them when viewing my creation through the first person shooter view. This is my first time with such a program so if there is something simple i need to click or adjust to make my objects react as solid could you please send me in the right direction or do you know of a tutorial online that could explain this in some detail? Thank you for your time.

Try attaching a Mesh Collider to you building model. Also you may want to remove the rigid Body, as that is for any object that you want to react to Physics Dynamically.

Components --> Physics --> & select "Mesh Collider"

add a mesh collider with the mesh as the building mesh

If you created an object from an external application, The mesh collider should work. don't use a rigidbody. Im assuming the character is using the first-person controller?

this really isnt an answer, just a really important comment.

really and truely, the first two answers on this page are correct. the last one has a few extra steps to follow, but i'm sure you could figure out,

but the first two answers are the easiest way to make the building collidable.