Answer:
Separation of powers were created to divide the government power and separate it into 3 different branches : executive, Legislative, and the Judicial branches.
Each branches has the ability to intervene with the power of other branches. So, if one of the branch want to use its power to hurt the people, the other branch could rise up and intervene.
Example of this would be the power to conduct a judicial review held by the Judicial branch.
The legislative branch has the power to create the law. But, before the law is passed, it has to be reviewed and examined through judicial review. If the judicial branch found that the law is constitutional, they can prevent the law from being passed.