Date Format for Creating Views

I am trying to create a view based on a date. I am not sure of the various operators available and would appreciate feedback. As an example, I want to show everything with a due date within seven days and overdue. The logic would be simple.... Show everything before 7 days from now that is open. So I would think the formula would be "Today +7d". However, I only get errors no matter how many variations I try.

Can somebody please tell me the date formats?

Also, if there is a list available of all possible operands that would be a great link for the forum.