What are the functions of central or federal government?

Well.. here in the USA, there are supposed to be strict limitations to government with the federal government protecting the borders and providing good defense for the people. These days the federal government does much more than that and doesn't do much of a job protecting the borders and some would like to dispense with defense (but who doesn't wish man was always peaceful and non aggressive?) - The federal government is supposed to be servant to the state governments (as you likely know, we have 50 states here!) And the state governments are supposed to be servant to the people of the state. These days that's getting eroded too, as all too often the government and, or a union for the government (for government workers) uses what is called "collective bargaining" and the people work to pay the taxes to support whatever it is the government decides! - Yes, my nation has come a long way away from the small government and strong limitations to government envisioned by the founders who tried very hard to create a system that would prevent oppression and tyranny, guaranteeing liberty, but these days, at least half the population has forgotten all those things and thinks a very large government bestowing many benefits is what is needed. But the other half (hopefully) realize a government large enough and powerful enough to "bestow" many benefits (as opposed to modest charitable programs to act as safety nets when citizens need them) is large enough and powerful enough to be a danger to liberty and more.