We won't go into the details of building a new block, if you want to go beyond themes, have a look at the book concrete5 Beginner's Guide, Packt Publishing or read the following tutorial:
The only thing we want to know is where a block can be found and what kind of files you'll usually find there. This knowledge can be helpful, even if you just want to customize the layout. Parts of the layout in your site are, of course, generated by the theme, but there are also parts which are created by different blocks. While an HTML editor block doesn't do much more than printing the text you've entered, there are blocks (such as the form block) where you have a more complex output, which might need a bit of styling.
There are four different places where you can find blocks:
/blocks/
: This is for blocks in the root of your website. This directory is empty unless you add your...