Click on the Create a Blank Notebook as shown in the below Image
Specify the File name and Select the Cluster which we have created.
A notebook is a collection of runnable cells (commands). When you use a notebook, you are primarily developing and running cells.
The supported magic commands are: %python, %r, %scala, and %sql.
Allows you to execute shell code in your notebook.
Allows you to use dbutils filesystem commands.
Allows you to include various types of documentation, including text, images, and mathematical formulas and equations.
For more details please refer Databricks Documentation.