Principal means first in authority; main participant, or amount of a debt minus the interest. It can be a noun or an adjective.
Examples: He is the principal stockholder….She is the principal speaker….The amount of principal is $200,000.
Principle means a basic truth or assumption. A lot of people think of principles in relation to ethics, rules, standards, morals, guidelines, etc. It is a noun.
Examples: The book revealed 20 principles for success in writing ….The country was founded upon those principles….She told her friend she wouldn’t cheat, since it was against her principles.
Perhaps the only time you can say, “I have my principals,” is if you are the parent of two or more school principals. Sorry. Couldn’t resist.