Its an evolution of the Swiss Army Triplet rudiment (you need to first figure out how to do this rudiment). Where, you replace the 2nd stroke (stroke immediately after the flam) with a 32nd double (lets say we're doing the Blushda in 16th note value). But of course you can do it in different note values relatively to the fundamental tempo you're playing in.
You can view Steve Holmes' explanation of the Blushda to deepen your understanding of the blushda as well.