I want to know how I can mare and date emails as sent. When I do it in the activity spreadsheet view I can add an email sent column but it wont let me add the date
If you are talking about the default column in the list view, then these are system fields and can't be filled manually. In this case, the last email sent is the actual date of the latest sent email (linked to the item).
If you are marking your emails as activities in the system and not using sync, then there is no specific one to mark the email type activity, but we show the latest and coming activity date.
An example of which fields I am referring to and they are all system fields: https://sharing.pipedrive.com/i/vfiGgx