What is best way to tell teens today the facts of life? Use ipad or app or face to face?

Face to face! The "facts of life" is so important and life changing that it cannot be relegated to an app. It must be done face to face and heart to heart to be effective and meaningful. Talk with your doctor or school counselor for assistance.
Depends. Some parents are uncomfortable talking with their teens. But it is best to talk face to face with people over important matters. You might use an app as a starting point. You can be sure they already know "the facts, " so your role is to support your child, discuss contraception, safe sex, and abstinence.