Someone wanted to learn this too, so Grasp built them a personal learning path.
You can keep exploring this one or create a path like this one shaped around you.
Recommended resources
Module 1
Foundations: The Two Faces of 了
Module 2
Mastering Completed Actions (Verb-了)
Module 3
Describing New Situations (Sentence-Final 了)
Module 4
Advanced Structures: 'Double 了' and Sequences
Module 5