Help in performing calculations in Zoho Creator fields

I have a particular problem, and I've been struggling with it. I thought I'd just go ahead and ask here.

I'm a book review editor, and I want to use Creator to track books I've assigned, review due dates, how many days a book has been out, etc.

Specifically, I have a field titled "Date Review Due." I want to look at another field, "Date Book Received," check to see if the reviewer has received the book, then look at another field, "Date Review Received," verify that the review has not been received, and then enter a date in "Date Review Due" equal to "Date Book Received" plus 30 days. I have another field, "Days Out," where I want to first check that "Date Book Received" is not blank and that "Date Review Received" is blank, and store a value equal to today's date minus "Date Book Received," so I can track how many days the book has been with the reviewer.

I'm sorry if this is so confusing. I can easily do this in a spreadsheet application, but I dislike the spreadsheet interface and much prefer the database interface. Can someone give me some hints as to how to build the formulas so that I can get this done?

Thanks so much!