They inherit it from someone in their family.
They get their power by elected leaders in a Parliament.
they get elected(not)
By doing good deeds.
When you say leaders, and if you mean kings, queens, etc, they take power by bloodlines, that is, they are appointed the next baron, king, queen, prince in succession, etc by being the next in the bloodline. Your question is vague though, as there are governing leaders in monarchies that are not noble themselves.
absolute monarchy
leaders take power in democracy through votes they obtain from the civil society
America today has elected leaders, whereas monarchy gives a country hereditary leaders.
One, mono.
"Pube Strummer."
Yes, they do.
A monarchy's rule is called a monarchy itself, which can take various forms such as absolute monarchy, where the monarch holds significant power, or constitutional monarchy, where their powers are limited by a constitution or laws. In an absolute monarchy, the monarch has almost complete control over the government and its functions. In contrast, a constitutional monarchy often involves a parliamentary system where elected officials share power with the monarch.
The source of power in a Monarchy is a royal King or queen.