Using initialization cells, you can specify that particular input cells of a notebook should be evaluated first. This ensures that your code is evaluated in the correct order, such as defining functions before evaluating cells that use those definitions.
Selected examples from the video:
This command requires the custom-defined function polynomialFunction to work properly. You can see that evaluating it without the function being defined produces an empty plot:
While it may seem obvious that polynomialFunction needs to be defined before using it to create a plot, it is easy to forget to define required inputs, especially when they are located in other parts of your notebook or are part of larger notebooks with many definitions.
The Wolfram System lets you create initialization cells to solve this problem. Initialization cells will automatically evaluate before other cells in your notebook.
To create an initialization cell, first select the bracket of the cell: