You "toe in" The front of the cleat seats into the pedal first, then you press down to spring the catch and capture the rear of the cleat. The pointer part of the cleat needs to be to the front.
You want to try and mount the shoe with out putting your foot in it. Then you can look and see hwat is going on.(You might be able to do this with your foot in the shoe, I am not that flexible) Look to make sure the tread of the shoe is not contacting the pedal anywhere, that can make it really hard to hook in.