How do I redeem a Vesteria code?

Excuse me, could you please explain the process of redeeming a Vesteria code in detail? I'm a bit confused about the steps involved and would appreciate it if you could guide me through the entire procedure. Specifically, where do I need to go to enter the code, and what happens after I do so? Additionally, are there any specific requirements or limitations that I should be aware of before attempting to redeem the code? Thank you for your assistance.