If you plead with someone to do something, you ask them in an intense, emotional way to do it.

When someone charged with a crime pleads guilty or not guilty in a court of law, they officially state that they are guilty or not guilty of the crime.

If you plead the case or cause of someone or something, you speak out in their support or defence.

If you plead a particular thing as the reason for doing or not doing something, you give it as your excuse.