How to integrate Office 365 in my application

Question

How do we implement the integration of Office 365 in my application.

Examples like:

1. How to open the Office 365 application from the web?
2. How to open an Excel or Word file using the Office 365(cloud app).
3. My application has export to file feature, how do I export it to the Office 365 directory?
4. How do I read the directories in Office 365 where the documents are saved?