Chaning the background color is fairly easy:
click on the foreground color picker at the bottom of the tool bar and select the color you want. Then use the maquee tool to draw a box around the background and hit ‘alt + delete’ to fill it with the color you selected.
To add text, simply click on the text tool and begin typing. you can change the text attributes (font, style, etc) in the character palette.
Hope this helps!
Amanda