To fill an area with color, you need to draw a shape to contain that color. It helps to have the color palette open too, which, if it's not visible, you can find under the Window menu (it's called 'Color' or 'Show Color', depending on what version of Illustrator you're using).
I'm not sure what your exact requirements are, but if you want to add an overall background color, do something like the following:
1. Open the layer palette (Window > Layers / Show Layers)
2. Select the lowest layer (there may be only one). If you see a 'lock' symbol beside it, you will need to deselect it first.
3. Use one of the drawing tools to draw the shape of the background (usually, just use the rectangle tool).
4. In the tools palette, you will see two overlapping squares at the bottom. The filled one signifies the color of the active object, while the other signifies the outline. Select the filled one, and choose a color in the color palette.
5. Choose Object > Arrange > Send to Back.
As for resizing, first you must make sure all the artwork is unlocked by selecting Object > Unlock All (if it's not available, it means there's nothing to unlock). Now select the artwork you want to resize -- in your case I presume that means everything, so if you're using AI 10, go to Select > All, or in AI 9, Edit > Select All. There are a few ways of resizing from here. A quick and dirty way is to use the selection tool (the black arrow), which brings up a bounding box around the selection. Drag any point to resize, but hold down the shift key if you want to keep the proportions.
You can also use the scale tool, either by clicking on it once to use it as above, or by double-clicking on it to bring up a dialog box to enter values manually. The settings in this box affect all scaling operations, so if you find that enlarging an object doesn't alter the outlines, look at these settings and make sure 'Scale Strokes & Effects' is ticked (or not, depending on what you want to do).
There are other ways of resizing too, such as the Transform palette and tool, but looking at the length of this post, I think I'd better stop before I confuse the issue!