As stated, if it is seizing, you are getting too much fuel in it. Make sure the tank isn't letting fuel flow in when it is just sitting. I have one plane that does that. Keep the tail low till you are ready to start it.

You could also seek help from the guys at your local flying field and they can show you how to start it. If you get too mucy fuel in it and spin it with the starter, you can bend the rod. Not a good thing.

Sounds like this is your first engine. I would seek help with it. Save the engine and the plane if they help fly it too.