The SA has three branches, the executive, legislative, and judicial, closely mirroring the national government. The executive branch comprises the president and vice-president, the legislative is the Senate, and the judicial is covered by the All-Campus Judicial Council, or ACJC for short. All full-time undergrad students are full members of the SA provided that they pay their student activities fee. Every full member can run for office, bring concerns before the senate, address the president, etc. The Get Involved page is a good place to start if you're looking into the SA government.