When you click on a puzzle piece, drag it to the area where the puzzle is to the space where the puzzle will be completed. Still holding the puzzle piece, right click on your mouse to rotate the piece until it looks as though it will fit somewhere on the puzzle space. Left click to place the piece into the place where the piece looks as though it will fit. If the puzzle piece has been correctly placed, it will briefly light up, and a sound will be heard.
Otherwise, if you continue to have difficulties, do a search on the Site link, and open the Chat window, which will connect you with a technical person.