Basic Block Development
What is the tools folder?
Generally, concrete5 has some scripts in the tools/ folder that are generally small scripts meant to be accessed from anywhere in the site. For instance, concrete5's upgrade script is actually a tool. The main tools of concrete5 are in concrete/tools/.
Blocks can have tools as well. If a block type has its own tools/ folder it might want to have some sort of pop-up dialog that does something interesting, or it might employ some means of interacting with the block outside of edit mode. It's kind of an advanced topic so knowing what that folder if for is enough for now.
Templates are alternate views for rendering your block. It's a good way to use the same data but present a totally different block. The usual way to do this is to just copy view.php into a folder named for your template, then make modifications. If you want that block's view.js and view.css to be available to the template, those need to be copied into the tempate folder too. Check out this how-to for a more in-depth look at templates.
Contact Info Block
The contact information block that Andrew runs through is not included in the core, but essentially all it is is a block that holds four text fields and one number for a File ID. It also uses the file manager interface, but that is discussed in the advanced block development videos.
Andrew also introduces a few more concepts that will be covered in Advanced Block Dev.
An interesting thing to note is that a block will not actually delete until the block is no longer referenced in any version of any page in your site. Otherwise the block record will persist so that rolling back to an older version of a page.