To use this join, you need one piece with loops on the edge: the selvage, cast on or bind off from Mary Thomas or Barbara Abbey, or the other side of the lacy tape, and an edge you are working. Note, I’m using the term picot to mean a loop on the edge, not a thorn shape.
Line up the picot you need to join to, if you are attaching different shapes to each other, you might need to skip some loops, I’ve been knitting a long tape to use as a measuring device, wrapping it around shapes, and counting how many loops and which ones connect.