Code Blocks are a hugely powerful core node that allow you to do many things by directly entering functions and code in the Code Block.

Code Block – String operations

Code Block String operations

Code Block – List methods
In the example below, various Flatten methods are shown in the Code Block. This would be an alternative to using the List.Flatten or Flatten nodes.

Source: https://twitter.com/Jos_ols/status/661822388112384000

More on Code Blocks at http://dynamobim.com/cbns-for-dummies/ such as: