Portaldomosphere

Create your blog if you have not already.

1. When you are signed in and looking at your blog, you will see a section to the right of the page called, "Edit this Blog" - right below it you will see a link called "Settings". Click this.
2. On the this page, click on "Theme"
3. Click on the button "Customize"
4. Click on the "Templates" link. Here you will see
1. "Weblog" - this is the main part of the blog. it handles all of the blog posts and everything except for the header and footer. 
2. "_css"  - this the style sheet for the whole blog. You can make all changes as far as style here.
3. "_header" and "_footer" - just as it says header and footer of the blog. Best not to touch these too much.

Best place to start customizing is in the "_css" page. Also, if you click on the "Create and Edit" tab, you will see a link to upload files. This would be the best place to put graphics and such. So for instance, what I did with my blog was to upload the question.png file the is on bleedyellow.com right now to my blog. Once I did this, I got the address of it and entered it in to the _css.
For Example - This is what is in my _css file :