Assume someone is a project manager in a project that is trying to create a rather massive solution.

Part 1:
The project manager has to define a process on how the project will proceed. This involves dividing the work into tasks and subtasks and defining a causal relationship between the tasks (i.e. in what order they have to be done, what can be done concurrently, etc..)

Question:
What functions are most relevant / most heavily used dividing the job into tasks, subtasks and creating the process which binds the tasks together?

Part 2:
Now the project manager has to estimate how much time it takes to complete each task and subtask in order to calculate a time table and cost estimate for the project.

Question:
What functions are most relevant / most heavily used in estimating the time and work effort it takes to do a task?