Hello, welcome to the wonderful world of betta keeping! :) This hobby is the best, believe me! :D Alright, what did you have in mind for a tank? It is reccomended on this forum that bettas have 2 gallons or more of swimming room. :) Filters rule, and heaters are a must.
Bettas don't really like flakes. ;/ They love pellets and eat them as their staple, but freeze dried bloodworms make their favorite snack ever.
Decor is easy! Gravel or sand, silk plants or real plants. :D Your choice! Real plants are more difficult to care for, but are rewarding for the tank ecosystem and look gorgeous.
Any other questions or things I didn't cover? :)