When done sending it the first time you will get a pup-up at the top right saying what it says in the picture.
After sending the command for the second time you will get another pop-up on the top right with your code in it.
(I have hidden mine on the picture)
When you got your code click on your profile on the top right on the website and click on settings.
then there is a box where you can enter the connect code to connect your in-game account to the website. 
Also after that make sure to link your discord account, it will also tell you this when you are trying to get something from the kits page/shop.