Athens did not have a king, it was ruled by the people as a democracy. The people of Athens believed that no one group of people should make the laws and so citizens could choose the government officials, and vote for or against new laws. The people of Athens chose their ruler.
They held a large meeting on the slopes of a hill in Athens where any citizen could speak, and tell the government what it should be doing. This was called the Assembly, and there had to be at least 6,000 citizens at every Assembly.
Athenian democracy was not like modern democracy. Only citizens over 18 could vote. Women, slaves and foreigners could not become citizens. So democracy in Athens meant rule by the men of Athens.
Slavery
Slaves made up about a quarter of the working population on Athens. Most were people who had been captured in warfare and sold to slave dealers. They were then put on sale in the slave market.