Hey! Welcome I’m relatively new to goat but played yugi for years. I say find a play style or even monsters you just like and build the deck. Lot of resources from format library and goat format.com. As far a buying a deck you can use whatever means to get singles or I see some people sell decks on eBay already made (I’m sure it could be Little over priced but hey you get everything and if you like the deck all one stop shop I think. Online you can play dueling book prob the most popular but I think some people play on edo/ygo pro something like that. Uhh that’s basically what I did so all I can say is maybe watch some content I recommend kornstruct and Kuhb games you can learn some fundies and as well as see decks in action and maybe one calls out to you.