To do this tutorial it would help if you know your 5ths, but it’s not essential.
Root-5th-root chords are just 5ths with the bottom note repeated at the top. That means that they’re always WWW or BBB, apart from B-F#-B and Bb-F-Bb.
Practice playing root-5th-root chords, focusing on the ones you find most difficult. For most people they’ll be the ones starting on black notes and on B.
Sign up to my Piano Chords course to learn how to use root-5th-root chords in context.