No legitimate free codes exist. Any site/video claiming "Free Xbox Live Gold Code Generator" or "Unused 14-day Trial" is a scam (survey fraud, phishing, malware).
Gold still required for 360 multiplayer (even F2P). No free codes. Buy 12-month key from CDKeys / Eneba / G2A (~$40–$50) — cheaper than $60 MSRP.
Never download "code generators" — they steal your Microsoft Account.