Video of Matt (founder of Think Maths) doing the 27 card trick, which explains the full solution of how the trick works: https://youtu.be/l7lP9y7Bb5g
The Cheat Sheet for the 27 card trick (shows you where to put ‘their pile’ each time in order to move their card to whichever position is required, if you call the positions 0 – 26):
https://www.dropbox.com/s/744gk02uw4ydts3/topmiddlebottomtm.pdf?dl=0