Nigeria is a federal republic whose government operates as a representative democracy. The current form of government was established in 1999, after the end of years of military rule. Much like in the United States of America, the president of Nigeria is head of the executive branch. The government also features a bicameral legislature and a judiciary branch.
The government and the president of Nigeria are vulnerable to corruption, just like members of any government. All in all, Nigeria has a relatively stable government that works to govern the country according to its constitution. In fact, the constitution of Nigeria has explicit clauses built into it to root out corruption. Clearly, this does not always get enforced.
Still, as a democracy, Nigeria holds elections to decide who holds office in government. Unfortunately, many elections in the past two decades have been the cause of violent events that put into doubt how fair and free the democracy really is. Patronage influencing and bribery are also frequent concerns.
In the end, though, it is safe to assume that Nigeria is still functioning mostly along the lines of its constitutional model. The different bodies of government are still carrying out their basic functions. Even with threats of violence and corruption, the members of the government are still part of a functioning governmental body. Just how truly democratic the government is, and how well it represents the will of the Nigerian people, is less clear.