How do I make my background transparent????

I know how to make an image with the background transparent but whenever I flatten the image and try to save it, the background returns to the foreground color????? I want to make an image so that when I save it, it doesn't have a white box around it. Thanks in advance!

you have to save it as a .gif
jpegs dont let you save with transparency.
Go to 'save for web' and there you can choose the extension that you want.
there are some other ones that Im not too familiar with, but .gif is the most common.

thanks! i'll try it!