Hello Basanta,
I'll do my best to simplify this. First, you can be assured that you're not the first to struggle with this logic. If you search through the PM Prepcast archive, you'll find several folks that have similar questions.
The easiest answer is that you need to consider all processes and process groups as iterative and cyclical. The PMBOK mentions this several times in each chapter, but it's difficult to really capture this in a linear (book) fashion. Here's what helps me: when I see Inputs that are also Outputs in other processes, and vice versa, I immediately understand them as cyclical. This is especially true with Project Documents (such as the Resource Calendar). Simply put, a resource calendar as an output to the Acquire Project Team and Conduct Procurements is pretty obvious (you just added resources), but how do we go backwards and use it as an input to the Schedule/Cost processes?
The answer is that you're only going backwards in the book; the processes are not that sequential. A resource calendar may be very basic at the beginning of a project, but it is consistently updated in any process that adds resources (making it an OUTPUT of that process). As you add or remove resources to your project, all those other processes you cited need to be updated too, so it becomes a very cyclical process. During Estimate Activity Resources, you may update the Resource Calendar but, even more important, define additional Activity Resource Requirements. These additional requirements may then become INPUTS into the Plan Resource Management process , then HRM Plan as an OUTPUT, then the HRM Plan as an INPUT to Acquire Project Team...and we're back where we started.
I hope that helps. As you get better at seeing the relationships of ITTOs from process to process, it becomes easier to pull yourself away from the "Step by Step" approach. Try to think more iteratively and cyclically.
