I have this exact pump. I was hesitant when I bought it due to its low gpm, however it said it could handle 9' of head so as long as I want pumping it upstairs I should be good.
I literally hooked mine up tonight, it did work, but slow. Like, slow. Tonight was only a test run and I didn't have any sparge so the slowness might be perfect, but as of yet, I question it.
Your issue is that you turned it on first. Pumps run on what's called an impeller, a small plastic or rubber propeller looking device inside the unit. It is highly recommended you don't run them dry, meaning without liquid at the impeller. This is because if the impeller gets to hot, it can warp and damage the seals that make it have suction. That said, you have to either, prime your pump with liquid from what is going to be pumped to the pump. It will NOT pull the liquid if there is air between the two, or it might eventually, but more likely you will break the pump. The better option is to set you pump at a level less than the top of your water line, like on the same plain or lower your kettle is on, open the valve and let the liquid gravity flow to the pump, open the valve to the next kettle it's going to, let the liquid equalize and then plug in the pump, it will take about 10seconds and you will hear the pump actuate and start taking the load, it will then start pumping the liquid properly. It is a slow pump, like 15 min to pump 5 gallons. It says 2 gal per min, but I don't buy it. Earlier I mentioned the pump is rated for 9 feet of head, this is a term meaning the uphill distance the pump will move liquid, so if you locate you pump a few feet or even inches lower then your supply keg, as long as your not pumping it 9feet up, you setup will should work.
On this pump your input is the lower one, and the output is the one pointing up. Hope this helps. Happy brewing.