I think it's described under the FAQ section, but basically you click on "advanced" in the lower right, and scroll down to "manage attachments", then a box opens that says "add files" and after clicking that you get "select files" which lets you choose them from your computer. If this doesn't help, the description may be in FAQ too. Most of us didn't grow up with computers and don't have a twelve year old around, so don't feel you are an idiot!
Kathy