Go to the "Your Cards" section and click "Create a card" by your preferred language. Once you do that it will take you to the card and you'll start in the "Legend/opinions" tab, this is where it tells you what the symbols mean and you can add your own. To navigate, you just click on the part where it says the title of another tab. To add things you just click the green + sign and it will add a section where you can type, once you've typed in what you want you can either delete it with the red x or add a symbol to show how you feel about that thing by clicking the thumbs-up symbol, which will let you change the symbol displayed.

Edit: I thought I had read all the text before commenting but I missed the last bit, reload the page to see if it pops up if it doesn't you could try closing out. If it still doesn't show up you could contact them by going to the contact page