During the software develpment cycle, when does the user documentation (writing User Guide, developer Guide or API Manual etc) starts? Is it after coding? Please give me answer in detail?
Hello Ghazal,

Welcome to the OutSystems Community! As you might know, we specialize in Agile delivery of projects so I'll be focusing my answer on that kind of methodologies. 

In a truly Agile software development cycle, documentation happens (if it happens) when it brings more value to the product as a whole. This means that you delay it until the last responsible moment and only produce it when a clear gain will come from it. Producing this documentation should also be as automatic as possible (check out OutDoc) and be derived from the actual code so that you don't have to keep documentation separately. Don't forget, in the Agile view of the world documentation is mostly a second class citizen that is not on par with running, tested code - the ultimate deliverable.

I really like this reference when it comes to Agile documentation. Take a look at it and it should help you better understand Agile documentation principles. 

Let me know if you need any more help,