Your post makes me remember the time when I had a class about methodology. In that class, I had to learn about second language acquisition, and comprehensible input is a part of that term. Unfortunately, I wasn't focused on class, so memories of mine were not sure

. But as far as I remember, Comprehensible input is a technique that helps you improve your second language level slowly but surely. For instance, I cannot force myself to watch a movie without subtitles if my level is Elementary or Intermediate.
You can search book about methodology to understand more about this term, but It's all theory

. And it's just a basic hypothesis that people are based on to change according to their needs. If you want to know more about teaching or learning English, you could search the keyword "ESL teaching methods" and maybe find the thing you need.