Mating A Curved Surface with a non-curved surface

Hello. I'm extremely new to SW so excuse me if this is nooby. I've a curved surface which I want to mate to the face of a non curved part. How can I do so? In the assembly I already have I merely shoved one part into the other with the triad tool but thats a pretty ghetto way to do it. Any help would be very much appreciated!

Warm regards,

Dar

SolidworksAssemblies