Governmentleader of a government and his advisors are called a regime. If they have a larger group of people who support them, these are a political party.
The simplest idea of government is those who rule some land. This may be as small as a village or as big as a continent (like Australia). Those people who rule the land can allow others to own it. It is a deed by government that gives this right in the way that laws describe. Some think they have the right to hold land without government permission. This view is called libertarian. Others think they can do so together as a group with others if they live in peace, without government. This view is called anarchist.
All land on Earth is controlled by one and only one government, except for some small border disputed areas. For every place on Earth there is a government that claims sovereign control over it. This way of speaking is old and means "control by a King" (sovereign).
It is from Kings and feudalism that modern governments and nation-states came. The capital of a country, for instance, is where the King kept his assets. From this we get the modern idea of capital in economics. A government is said to regulate trade as well as to rule over land.
Governments also control people and decide things about what morality to accept or punish. In very many countries, there are strict rules about sex and drugs that are part of law and offenders are punished for disobeying them.
There are many theories of how to organize government better. These are called theories of civics. Because government is very dangerous, most people think leaders must be elected by some kind of democracy.
There are many theories of how to run a government better, and reduce harm people do to each other. These theories are part of politics. No matter how a government is chosen, it must do politics to keep power.
There are many ideas about how to settle a dispute without needing force or violence but by talking and trusting. This is part of ethics. When religion convinces people not to fight or rely on government, we say an ethical tradition is at work. Most law comes from traditions like that. The Ten Commandments is one group of laws like that .