The previous lesson (metal-double-bass-basics) introduced both feet at 8th-note speed. This lesson zooms back out to the slowest possible double-bass tempo — quarter-note alternation, RLRL — so the non-dominant foot has time to learn what it's doing. Two pedals, one note each per beat, no rush.
Why bother going slow when 8ths are easier than they sound? Because the L foot is what limits you. Most beginning metal drummers can fake 8ths with a heavy R and a weak L, then hit a wall at 16ths because the L was never really pulling its weight. Quarter-note RLRL forces the L to play alone on beats 2 and 4 (or whichever beats you assign to it), which exposes the imbalance and gives you a tempo where you can fix it.
Notation Note
Both kicks are notated on the same line (f/4) — the kit usually has only one kick voice, so even with two pedals, one notehead per stroke is all the staff can show. The R / L split lives in the tip text, not in the notation.