From where to start for studying

Hello All,

We have got a new project wherein we have to implement IDoc-to-IDoc scenarios on SAP PI 7.31 Single stack.
Kindly provide me some links wherein this scenario execution is explained in detail.

Thanks,

Ajeya G V

P.S, I have 3 weeks of time to learn and study and I'm a beginner so please provide me links wherein the explanations are given in such a way that even a beginner can understand.