How to redeem GSC voucher code?

Excuse me, I'm a bit confused about the process of redeeming a GSC voucher code. Could you please guide me through the steps? Is there a specific website or platform where I need to go? Do I need to create an account or sign in to redeem the code? Also, are there any limitations or expiration dates associated with the voucher code that I should be aware of? I'd appreciate it if you could provide me with a clear and concise explanation. Thank you in advance for your help.