[Pulz]

No need to guess, the very first header is 'How It Works'..

[pluto_modadic]

that's not a visual guide, and the thumbs along with above and below mentioned are confusing.

[smeej]

Your thumbs run vertically along the sides of the card, parallel to each other. You use them to cover anything to the sides of the month header(/footer) you're looking at. I think it's that "not under or above" description from the link that's confusing.

Find the header/footer for the right month. Use your thumbs to cover everything to the right or left.