Learning Resources for Recommendation system
If you have a technical background, I would certainly recommend the chapter 9 from Mining Massive Datasets by Jure Leskovec. Video lecture of the topic is also available there. Look for chapter 9. This blog could also give you some overall insight.

Please keep in mind that, ML-wise, recommendation is a more creativity-related topic than other classic questions like Classification or Regression and indeed all those classic problem could be a step in building a reasonable recommender engine.