If you initiate something, you start it or cause it to happen.

If you initiate someone into something, you introduce them to a particular skill or type of knowledge and teach them about it.

If someone is initiated into something such as a religion, secret society, or social group, they become a member of it by taking part in ceremonies at which they learn its special knowledge or customs.

An initiate is a person who has been accepted as a member by a particular group or club and been taught its secrets and skills.