Protein skimmers are actually pretty simple. The pump at the bottom creates foam by mixing air and water. Proteins from animal waste stick to the outside of the resulting bubbles and are carried upward where they pop leaving the protein floating on top of the foam mixture. Eventually this protein layer becomes thick enough that it gets pushed up and over into the collection cup. This can then be emptied and cleaned. Do be aware that most protein skimmers take several days before they produce much, it takes time for enough protein to accumulate at the top of the collumn to overflow. Also in a heavily stocked, heavily fed tank a skimmer will produce more, in a lightly stocked, lightly fed tank it will produce less. Provided you've adjusted the air intake to pull the right amount of air versus water to have foam rising to the top of the mixing chamber (b) it should work. All you should be seeing is foam in the mixing chamber and possibly bubbling up into the collection cup. If I understand the diagram correctly, you will need to attach the small air intake on the pump (bottom left arrow) to the air intake valve (a) via airline tubing. If you are having issues, make sure you did this. Good luck!
