Today, I slept for six hours on the comfortable green sofa.

We use on for surfaces, including most furniture you sit or lie on (like a sofa or a bed).

Then, I meowed loudly at the front door until the human opened it.

We use at for specific points in a space, such as a door or a window.

Finally, I took another long nap in the kitchen.

We use in for enclosed spaces, such as rooms in a house.