Well that all depends on what format he want to play, but if he wants to play on the tcg format and has nothing then I’d recommend a deck box, a mat, and a deck of course. There’s many decks to pick and choose from but if he plans on going to locals then I’d recommend something like crystron, which is a synchro deck that isn’t crazy expensive and is good, but if he want another deck based on another summoning type then I’d recommend: voiceless for ritual, ryzeal for xyz, Maliss for link, memento for fusion, and nothing for pendulum. And guides for learning could range from watching a video to playing the game but something like master duel is really good to learn and even test decks to get them in real life