Now to add it to your blog.
Log into your blog and on the left hand menu select 'layout'.
On the layout screen click on edit in the box that says 'header'. This lets you edit your blog's header.
You will get a pop up window that looks like this:
Clicking the choose file button will allow you to select the image you want to use for your header. Under placement, select the second option 'instead of title and description' - this means that you will get the image only and no text over the top, it will show up exactly as you have designed your image. And check 'shrink to fit'.
At the bottom it mentions the size your image will be shrunk to. Make a note of the number of pixels it says, you might need this later.
Back on the layout screen, click 'view blog' at the top and take a look at your handy work. Impressed?
If everything looks hunky dory, congratulations. If not, don't panic!
When I first added my header image it cut it off slightly:
You'll see that the right hand edge of my picture is missing, because it was too big to fit the gap. Alternatively, you may have found that your image is too small. This is easy to change.
Open up your header image in paint and click on 'resize'.
[If the number already in the horizontal pixels box is much smaller than the number you made note of, then increasing the size of the image may make it go a bit fuzzy. In this case, you will need to go back and edit your original image to increase your canvas size, in whatever programme you used to create the image.]
Then repeat these instructions, uploading your newly sized image. It should fit perfectly now.
Next I suggest you add a followers gadget so that you can start collecting followers.