Theme Builder is extremely powerful in my modest (but correct 
) opinion. You can use it to create nice looking, simple layouts or if you use it in conjunction with css you can use it to build complex designs.
My top tips for learning how to use Theme Builder
Your starter for 10 : complete any of these step by step tutorials :
The adaptavist theme is particularly useful if you need to know how to create a more complex theme. It will show you how to access the various div hooks in the layout to create the rounded edge design that you can see in this theme.
For your Main Course : Refer to the many pages of documentation that we have on our web site.
The documentation pages that I refer to the most and that you will find incredibly useful are as follows:
Layout : Panel Classes and IDs
The Panel Classes and IDs page is a gem and supremely useful for css class names in Theme Builder. To this I add a piece of advice : be specific. If you can't make a css style take effect, specify the class name of the containing element. We get asked this question all the time, "Why are my css styles not taking effect?" The answer is:
Not just
h1{color:#000;}
but
.atb-header h1 {color:#000;}
Links
Compound-menuitems
You want to add links to parts of Confluence (For example, Space Admin or My Profile etc.), to other wiki pages and use icons and plenty other useful stuff? Use Compound-menuitems.
See also Links Reference if you need to more of the link names for various parts of Confluence functionality (for eg. Login/Logout)
More to follow.......
