how to calculate power budget calculation for new project? Need basic steps to start
When you are in the early (preliminary, feasibility) phase of a project you can make a very rought estimate based on similar projects done in the past, or by (tentatively) inditifying the most power-hungry sub-part(s) and calculating their consumption. Multiply this for instance by two for a margin. If the value you come up with does not raise any eybrows power will likely not be a problem in your project.

In later phases you divide the total power budget into what seems reasonable for the subsystems and give that as a budget for each subsystem designer. He designs according to that spec and everybody is happy.

Things get more interesting when power (or any other resource) is scarce. That requires (system) engineering, which is not something that can be explained here, even a book would not be sufficient.