A free original bilingual lesson on selected coding and decoding models. Check fixed shifts against every example, reverse an encoding direction, keep intermediate stages visible in a position-dependent rule, and use direct letter-to-digit or unordered word-code mappings under stated conditions. Distinguish a determined target from insufficient information by considering different consistent mappings. Five worked cases, two unscored completion pauses, an analogy, a quick reference and five explained questions develop these skills. Code-bearing English words and tokens stay unchanged in Hindi so the evidence remains the same. This is reasoning practice, not real-world cryptography instruction, an official past paper or complete coding-topic coverage.