1 - First, you need to access the wargaming website (valid for World of Tanks / World of Warships / World of Tanks Blitz) --> wargaming website
2 - Click on "Log in" in the header at the top right of the site.
3 - Enter your Wargaming credentials (You will be redirected to a login interface)
4 - Once logged in, click on your username in the top right corner, then in the window that opens, click on "Activate a Wargaming code"
5 - All you have to do now is enter the code you acquired. Please note that there must be no spaces and the capitalization must be respected.
If your code is valid, you will see the message "Code activated" and possibly its contents, depending on the code.
Note that some codes are consumables and others are missions. Remember to check the entire interface to see what has been activated.