The principle of checks and balances is a system that ensures no one branch of government becomes too powerful by allowing each branch to limit the actions of the others. A classic example of this principle is:
The ability of the President to veto legislation passed by Congress.
This action allows the executive branch (the President) to check the power of the legislative branch (Congress) by rejecting laws that they have approved. Conversely, Congress can override a presidential veto with a two-thirds majority vote in both houses, showcasing another layer of this system where the legislative branch can check the executive branch's power.
If you'd like more examples or further explanation, feel free to ask!