Assembly to Part

I'm a self taught SW user and working on a project I needed to assemblies and wanted to mate them together so i kept the assembly and changed the assembly to a part and then tried to mate them. The issue is when i converted the assembly to a part the new parts are not moving  + there is a dark blue color box in front of the all the part specification, which I'm not able to understand why. 

SolidworksEducator / Student