First steps with Google Apps Script
Where you paste a script, how you allow it once, and how you add a time or form trigger.
Where the code lives
Open the sheet. Extensions, then Apps Script.
Delete the empty function, paste the code, save.
The first run asks Google for access to the sheet and, if the script sends mail, to Gmail. That is once.
A trigger
A menu starts when you open the sheet, if the code has onOpen.
For a form: Triggers, Add trigger, On form submit.
For a daily reminder: Time-driven, Day timer.
If a column has a different name than in the code, the script stops and tells you which one is missing.