AC is not needed to enjoy the game. Most items that are purchasable using AC are either cosmetic in nature or items to improve convenience.
AC is not required for character leveling or progression.
Select [Main Menu] → [Shop] → [AC/SG Shop] → [Charge AC] to purchase an AC Exchange Ticket from the Microsoft Store/Steam Store/Epic Games Store. Once the AC Exchange Ticket is purchased, the AC should be added to your account. Please read the notifications and description in the Microsoft Store/Steam Store/Epic Games Store when making your purchase.