Auto-triggering of PM Planning from service contract

Greetings!

I am currently working to automatically trigger preventive maintenance service order from service contracts. However, I have been struggling to understand some of the dates and the date rules, and how they work?

The dates are:

                                                    Rule Name

a) Planning start date:                  Today's Date

b) Planning Date From:                Determine Planned Date

c) Planning Date To:                    Planned Start + Tolerance

d) Start of Interval                        Planning Start Date

e) Service order creation date:     Planned Date - 2 weeks

f) Tolerance:

Let's say that I would like to have a contract valid from the 13.08.2014 to 13.09.2015, and I want the preventive maintenance service order to be begin from 20.08.2014, with a interval period of every 2 days (may be until 10.09.2015). Then how should I fill these dates in the service contract item ?

I would be glad if someone explained it to me. If you have a better example, I would also appreciate that.

Thank you.