Custom blocks can be created, in addition to the default blocks that already exist in the system.
Custom blocks can contain all of the same content that the Body area of your nodes contain. Keep in mind, though, that blocks that are placed into a narrow area, such as a sidebar, will require narrower content. Digital assets such as images and video players will not automatically resize to fit in a narrower area so you must resize them accordingly or the item will spill over the edges of the block.
There are a couple of different ways that you can add a block...
If you are not already within the Blocks manager, you can add a block directly from the Admin menu by going to Admin menu > Site building > Blocks.
If you are already in the Block manager, just click on the Add block tab at the top of the page.
Once inside the Add block panel you will note that it looks very similar to a node submission form in the fact that it has a Body field with a WYSIWYG toolbar and the Input Format fieldset.
The only real difference between a custom block and the default settings you see on something like a simple menu block is the presence of the Body field. All other default block configurations, as described in the General Block Configuration section of this manual, are present.