The video discusses Stephen Krashen's language acquisition theory, emphasizing that language acquisition is a subconscious process, while formal learning is a conscious effort, with the former being more effective. It explains that grammar elements are acquired in a specific, natural order, regardless of teaching methods. Krashen’s Monitor Hypothesis suggests that knowledge of grammar has little impact on language acquisition and can even hinder speaking. The Input Hypothesis stresses that comprehensible input is essential for learning a language, with speaking alone not being enough. Krashen advocates for teaching methods like Total Physical Response (TPR) and immersive platforms like LingQ, which provide gradual, comprehensible input to help learners improve over time.