Your spreadsheet, with FormEmailer set up, have at least two sheets. If you look in the bottom left of your spreadsheet you should see some buttons to select each. Something like: "Sheet1" and "FormEmailer".
Click on the FormEmailer sheet to open it. Then, click cell A5, that is probably merged with a lot of other cells adjacent to it, in a big white space without grid lines.
Then, after selecting these merged cells, look on the spreadsheet toolbar for a icon labeled "Break Apart", and then click it.
You should now see the instructions on how to set up the trigger.
Regards,
Henrique G. Abreu