Unlike a regular corporation, a nonprofit corporation does not have stockholders. This is because nonprofit corporations do not issue stock. Instead, nonprofit corporations can choose to have members.
A formal membership structure often grants members certain basic rights, such as the power to vote for directors and approve a sale or merger. Most nonprofits (especially smaller ones) do not have members, due to the additional paperwork and required formalities.
Even without members, other people may still participate as advisors, patrons or contributors, but without a formal vote. However, if your nonprofit is a club or social organization, it might make sense that all of the members have a formal vote on certain important matters.