Like the first two puzzles, there are clashes between sidechains when this one starts. This puzzle introduces the shake tool. Shake automatically moves all the sidechains, trying to find a better position.
To solve the puzzle, click on the shake button in the lower left of the window. The clashes should clear. Click on one of the stop button to finish the puzzle.
Technical stuff: this puzzle shows two helices (or maybe "helixes"). The two helices are connected by a section of loop. The two previous puzzles had only sheets. More on helices, sheets, and loops later.