From the moment you begin envisioning founding a nonprofit, you must think about developing a board of directors. As you go out and talk to the community about your plans, you will find out who shares your sense of mission and also is well-connected and capable of serving on a board. Before you register a 501(c)(3) nonprofit, you do not need a formal board, but organizations sometimes form an advisory board to get them through the launch phase, then switch out to a formal board.
The pages ahead will explain the role of the board in your governance: how you recruit people onto an advisory board who help you draft bylaws, which establishes and is approved by the board of directors that then holds financial and legal responsibility for the organization.
How to get tax-exempt status is covered in the next chapter.