The text is describing Hanayama puzzles. If you don't recognize them, you might find their site via searching for "violin puzzle piece", say.
The normal page you wind up on shows all the puzzles on one page.
Steps
First, focusing on the larger piece, align the other piece's gap so you can move it rightward from the upward pointing triangle to the downward one.Describes Cast ABC focusing on the AB piece.
Then, with the critical piece's non-gimmicked nut fully lowered, slide the narrow section of the other piece (where the sculptor's copyright is) past the nut.Describes Cast U&U focusing on a U piece.
You should notice that one of the two little bar ends on your piece's end curl is squared off versus rounded, which gives you enough clearance to untwist it from the other piece's identical curled end and leave it hanging from that piece's middle.Describes Cast S&S focusing on an S piece.
Next, turn the sculpture so that the larger piece is vertical, side on to your vision, and slide it past the violin shape.Describes Cast Violon, manipulating a rectangular piece to look like an I from your point of view.
With the notches on the other two pieces (labeled with one dot and three dots) aligned, you can pull the (formerly middle) piece past them and out, facing you with the open side up.Describes Cast Chain, ensuring that the piece is held so it looks like a V.
Finally, arrange the two “ocean wave” shapes on the two pieces into the two curves on the other and remove the critical piece with the tiny hanging loop (but otherwise identical), making sure the tiny loop is in the upper left.Describes Cast Baroq removing one of the pieces in the right orientation to look like an E.