So, you have the Essentials Kit?
That's great to hear! Within the box are a few codes for D&D Beyond. So, how do you redeem those codes? First you will need to go to this page.
Once there, you will need to carefully input the code from your flyer.
PLEASE NOTE: The codes are case sensitive. Some letters in the codes might be a bit deceiving as well. If you can't get your code to work, please check if that O isn't a 0 (zero), and l could be a 1 (number one), lower case L or uppercase i. If you are still having issues with your codes, please contact Customer Support. Please include a picture of the code(s) you are having issues with, to better help the Support Representative locate your code.
Enjoy your new content on D&D Beyond!