For example, this picture on the left is a room. You might notice that there is a background. A background is similar to a sprite except you don't need an object. (See previous blog entry for explanation of a sprite). This means that it is just a picture, but you can't tell it what to do. If you look close, the clouds are all similar to each other. If you look even closer, you will notice that some of the clouds are the exact same as others. This is because the background is made in tiles.
If you noticed, this is a close-up on one of my game's rooms. It might be easier to look at the clouds now.
This is a different room than the others.
As an example, the background is different. Also, you might notice that there are arrows telling the player what the controls are.
This is a different picture of the room above. You can see the background clearer now. And now you can see that the walls are different. A wall is a solid and it doesn't have to be on the edges. It can be anywhere. Some people might program it differently, but people usually program it so the walls prevent the player from coming out of the room. You can also use them as obstacles in the room to bother the player. As you can see, the giant mess of walls in my game pretty much block most of that part of the room.
You can't see this, but in that gap in my game at the bottom there are actually blocks that when you hit them, you go to the next room. I plan to have at least 25 rooms in this game. I have done at least 8 now. You might think I'm crazy when I say at least 25 rooms, but rooms are actually pretty easy to make. The programming is the hard part. (See my first entry). For me, the programming is pretty hard, because I have to teach myself how to do it.