Principal vs principle

As a noun, principal refers to (1) one who holds a presiding position or rank, and (2) capital or property before interest; and it’s also an adjective meaning (3) first or most important in rank.

Principle is only a noun. In its primary sense, it refers to a basic truth, law, assumption, or rule.

Eamples

Principal
The head of a school or college is a principal.
The upcoming production of the ‘The Roomers’ is now casting for principal actors.

Principle
Although Rule 11 applies to only federal courts, the same principle applies to all plea hearings in all courts.
It is a fundamental principle in the modern world that disabled people should be given the opportunity to participate in modern society.

Source: grammarist.com