Using the development environment – the script editor
The script editor is a dedicated online development environment that allows for text editing, automatic code formatting, and basic error detection, it can be opened from the tools menu of a spreadsheet, the tools menu of a text document, or directly from the Google Drive home page at https://drive.google.com | Create | Connect more apps | Script. This last document type is optional in the drive interface, but once you have it activated, it will remain available. I strongly recommend that you do so if you are interested in Google Apps Script.
For now, we will use the spreadsheet interface, open the script editor from the Tools menu, and write the code snippet we just prepared.
The script editor ...