Once you claim the code via Samsung Wallet. You will have until May to redeem the code on Disney+.
If you click the voucher on wallet, and click 'redeem' it should direct you to login/register an account with Disney+ and you will get the 12 months subscription free of charge.
I believe if you have a current subscription with Disney, you will need to cancel this in order to redeem the code.
If you don't redeem the code, you will lose it and will not recieve another.