Paste your 32-digit voucher code. The page then shows the voucher value, so you can check the amount first.
Next, add your email address in the Basic details step.
In Address details, pick the coin you want and paste your wallet address for it. Check every character carefully, since nobody can reverse a blockchain transfer.
Finally, review the fee breakdown, tick the Terms box and click Redeem. The crypto usually reaches your wallet within about 30 minutes.