A monarchy is when there is only one ruler of a civilization, and power is inherited after the king's death, going to another family member as inheritance.
I live in Ancient Greece, in a monarchy. In my community, we only have one person to govern the civilization, most likely a king. When our current king dies, ruling will go to one of the family members as inheritance, and will go on as a cycle until a change.
We live in an oligarchy. We govern with three people. The thing we like to have the most is wealth, and we have made poor people poorer to get wealthier and had no care for people's rights. We could only be taken over by force.
An oligarchy is a community ruled by the few. Unfair laws and requirements are made and poor people become poorer. Must be taken over by force.
I live in a tyranny. I am a soon-to be tyrant, someone unlawful of power. I gain trust by promising citizens that there will be more food and supplies etc if I am put in charge. I gain support from the military, then this is when I take power by force. The things I promised do not come, and I harshly rule the community with unlawful ruling, ignore peoples needs, and to lose power I must be overthrown, or taken over by force.
A tyranny is a community ruled by an unlawful king. This unlawful king rules by showing promising prompts that there will be many advances if they are put into power. If successfully they gain enough support to rule the community, they make unfair laws and do not consider any citizens needs and must be overthrown/taken over by force.