Upon purchase, you'll receive TWITCH account.
Link it to your game account to claim the following items: 

1. Mask of the Watcher Mask
Code can only be activated on the official website https://www.minecraft.net/en-us/redeem

NOTE: 
!!! Claim items promptly post-purchase; they may expire.
!!! Unlink the Twitch account once all items are collected.
!!! Items hidden after 6 months are still claimable.

This code can only be used once on one account. Suitable for all regions. Please note that to receive the item in Java you will need to log in to the Bedrock version of the game. 
Please receive items on your Minecraft account immediately after purchase.