"Principal" refers to a person in a position of authority or the primary part of something. "Principle" means a fundamental rule or belief. Ex.: The school principal addressed the students. The principal reason for our success is teamwork. Honesty is an important principle to uphold.

"LED" and "LEAD"

"Led" is the past tense of the verb "to lead." "Lead" can be a verb meaning to guide or a noun referring to a type of metal. Ex.: She led the team to victory. He will lead the project. The pipes are made of lead.