Element and set are two different definitions. An element refers to one, and a set is made up of many qualified elements (finite or infinite).

It is estimated that you are conscious of the content of senior one. Let's give a simple example:

You are a member of your family, so is your father, so is your mother, so is your grandfather, so is your grandmother … Then all of you form a complete family. So each of you is an element, and your family is a collection, can you understand?