You can launch the Google app script editor in google spreadsheet by following the below steps:
Login into Google drive https://drive.google.com with your Gmail username and password
Select “New”-> “Google Sheets”. You can find an “Untitled Spreadsheet” in new tab
Click on the “Untitled Spreadsheet” to change the name of the google spreadsheet. Give a name to your spreadsheet. Here, I gave “My Google Spreadsheet” as spreadsheet name.
Go to Tools-> Script Editor to launch the script editor page in new tab.
Your new script editor window will be launched as shown below:
That’s it!! You’ve launched a script editor page.