[2019] Where to redeem codes?

@Trifler#68868:

It seems the in-game store doesn't show up until you complete the tutorial.
When I click on the link in the e-mail, it opens a web page with a field to input the code for about 1 second, then it switches to the home page of the MTG web site. I don't know why it does that.

You can skip the tutorial in the settings menu!