Primary resources
Here is a concise explanation of Newton's second law:
This is a comprehensive introduction to Newton's second law that covers how to deal with Newton's second law and systems. This online textbook discusses Newton's second law with diagrams, worked problem examples, and interactive conceptual questions. All notation in this text is consistent with KC's:
NASA video introducing the concept of Newton's second law:
https://www.youtube.com/watch?v=WzvhuQ5RWJE
Doc Shuster's introduction to Newton's second law part 1:
https://www.youtube.com/watch?v=dFybXASirwQ
Doc Shuster's introduction to Newton's second law part 2:
https://www.youtube.com/watch?v=_Z7qivqbSBI
Here is a really great video by Dr. Davies from Gordon State College that relates a physics problem, Newton's Second Law, and FBD:
https://www.youtube.com/watch?v=NDiQ363uBj8
Other Resources
This page on PhysClips discusses many aspects of Newton's Law and most importantly to you the limitations of the Laws.
Bozeman on 2nd law: https://www.youtube.com/watch?v=2qdW0RSFHps
NSF football 2nd law: https://www.youtube.com/watch?v=qu_P4lbmV_I&feature=youtu.be
Here is a really great video by Dr. Davies from Gordon State College that relates a physics problem, Newton's Second Law, and FBD: https://www.youtube.com/embed/NDiQ363uBj8
Lecture video highlighting general steps to solving mechanics problems: Video