Here is my booklet on "Les articles". This has been tried and tested with my Immersion classes.
In this package, I have included an overview of what "les déterminants" are, on articles being part of "les determinants", the four types of articles, exercises, and a quiz to solidify understanding.
Although I haven't included it in my package, I have verbally explained to my students that "de" can sometimes be a determinant or a preposition.
A good little resource to use at the junior level to cover the basics.