You will receive a code that is redeemable for the booster pack above on the Pokemon TCG Live service. You will not receive any physical product mailed to you.
The PTCG Live game limits the number of codes that can be redeemed per account. There's a 400 pack limit you can redeem for any particular set (booster pack codes). Any additional codes you redeem give you Coins instead of booster packs.
Upon purchase you will receive a separate email from firstname.lastname@example.org with all the codes ordered. This email may end up in your spam folder.