Content blocks/Blocks is a custom posttype which allows you to create a page/block/module using visual composer. You can use the content block modules to almost anywhere in the website such as footer.
All blocks can be used as a shortcode on every page so it helps you to repeat the same module to multiple times in different pages. If you modify the block, changes will be applied to all pages’ module at a same time.
You can create new content block at Blocks/Add New Block