The Overarching Structure of The Project Management Office Discussion

I’m working on a management writing question and need the explanation and answer to help me learn.

Respond to the following:

Considering the overarching structure of the project management office (PMO), portfolios, programs, and projects, what are the dynamics of team formation for each of these areas? What external and internal factors would be considered when forming a team within each of these structures?

How might your career path in the project management field include program or portfolio management?  I work in the financial world of software change.