Q:

How to copy object(s) to another layer

I am building a model for a game and have decided to copy part of it into a separate layer. How do I copy one or more objects to a different layer?

A:

To copy an object you have to be in Object mode, right click on the object that you want to copy and the press Shift + D to duplicate it first. 
The duplicate will be in grab mode so right click to get out of grab mode without changing its location. 
The object will still be selected but if it isn't, you can look in the Outliner for it. It will have the original object name followed by a number indicating that is a duplicate such as Object.001.
You then press M to bring up the layer move popup menu and click the button for the layer that you want to move it to or alternatively type the number corresponding to the layer.

A:

Select the objects that you want to move and press M, then select the layer you want to move them to. You can also have an object in several layers, for that after pressing M, Shift +  LMB select the layers.

