I'm a total newbie when it comes to custom layouts and headers, but I did recently manage to make a simple layout and header for this blog. It's nothing fancy, and nothing like the beautiful blogs many of my blog hereos have, but it is custom and I made it myself, so I wanted to share my new found knowledge with all of you.
I began my search by just googling "make your own blogger layout" and sifting through the different tutorials until I found one in simple enough language that I could follow it.
For a custom background, I used the tutorial on SJH Blog Design, and it was perfect. I won't rewrite everything she wrote on her tutorial; just go there and follow the instructions for how to make a custom background.
For the header, I found that her instructions were too complicated for me, and I couldn't get them to work. Instead, I used a digital scrapbooking program called Memory Mixer to create the custom header just the way I liked it. You can use any photo editing program, like paint or photo shop, etc to create your header. Then, on your dashboard click 'layout' and then click 'edit' under the header portion of your layout. A window will pop up prompting you to chose an image. First, choose 'instead of title and description' and choose 'shrink to fit'. Then, it will ask you to choose an image from your computer or from the internet to add as a header. Choose the header you made previously from your computer and click save.
The final step is to change the color of your font to the color of the paper where your blog text is written. Again on the layout page, click 'fonts and colors' and then choose an exact match from the color choices for the option 'border colors'. This will ensure that there is no border around your header.
I hope this helps someone!