Idioms are phrases which mean something different from the meanings of their separate words.
For example to grease someone’s palm does not mean to put grease on the palm of someone’s hand.
It means to bribe someone.
Here are more examples
Examples of sentences using idiomatic expressions;
Idiomatic expression;all things to all people
She's exhausted tying to be a good wife, a good mother and a good teacher, but she can't be all things to all people.
Idiomatic expression; apple of your eye
Angel is the apple of your eye and me too.