Need help setting up skimmer

I've never set up a protein skimmer before. Perhaps I'm not very intelligent or something, but; today I bought a Eco Mini 28R with the refugium cut out so I could put a nice size skimmer in the back. The skimmer i got with it is a Aqua Euro USA Hang on Back model number AEBH100 with an MJ1200 pump. I filled the tank with water made sure the back of the tank had the same level amount and filled the skimmer a bit and plugged it in. I hear the pump churning but suddenly the water starts flowing back into the tank. Thankfully i wasn't left with a flood. Someone please help me out.

 

Can you get a picture up please?

as it might be a issue with not introducing air into the skimmer - hence you get a lot more water

Im not sure on the Aqua Euro HOB,
but it looks like a Reef Octopus and for mine there is an air line tube fitted to the pump inlet so that the pump pulls in air as it pushes water (venturi)

if you only partially filled the skimmer the pump may struggle to fill the rest due to back pressure so you need to completely fill the skimmer so the level in the skimmer is about level with the water outlet back to the tank
then plug it in and it should circulate water
and bubbles should start filling in the body of the skimmer

if there are no bubbles, you need to make sure your air line is clear and not closed or trapped

Steve