SBCs are puzzles where you submit a squad of players that meet specific requirements (e.g., minimum chemistry, maximum rating, specific leagues) in exchange for rewards like packs, coins, or special player cards. They are a great way to utilize untradeable players or those not fitting your main squad.
Always check the rewards and requirements carefully before committing players. Some SBCs are repeatable, while others are one-time. Use online resources like FUTBIN to find solutions, but try to solve them yourself first to save coins. Completing daily and weekly SBCs can be a consistent source of income and new players.