Jij bent - you are (informal)
U bent - you are (formal)
When to use jij or u depends on the person you are speaking with and the country as well.
In Belgium people tend to use the formal u much more often. Even parents to their adult children.
In Holland people are more informal en use jij far more often. Even in stores people often use jij.
You use u with
- job interviews
- talking to people with high position
- elderly persons
Nowadays I often hear elderly persons saying that you can talk with them using u in stead of jij.