Both Merge/ Inheritance and Copy Geometry options are located in the Get Data Group in the Model Tab.
The Merge/Inheritance feature is the way you incorporate one complete solid part into another solid part. The result is a single feature added to the target part. When setting the feature to the Merge option, no changes are allowed in the new part. The Inheritance option allows access to the individual features, enabling you to edit the Inheritance feature in your new part. You can use the Merge/Inheritance feature to handle cast and machined parts. The Merge/Inheritance feature will also allow you to make Cut Outs. You can use this functionality to make assembly nests or other such fixtures.
The Copy Geometry feature allows you to copy features and references from one part to use in another part. It is indispensable in top-down design, where you want separate parts to share common references. You can use Copy Geometry option to copy the internal surfaces of a cast part and incorporate them into a separate part that represents the core. Once the surfaces of the inside are in a new part, you can close them and use surfacing tools like Solidify to make a representation of the core.
These topics and more can be found in our Creo Parametric Advanced Part Design and Creo Parametric Advanced Assembly Design and Management courses.