Making assembly:
1. select the part that you want to be assembly, then click file-Save as Assembly.
3. You're going to get a window under Assemblies folder. give the name of your assembly and then save it.
4. You're going to find it in the Catalog explorer, under Assembly.
*Attention:
(1) if the line connected with OPC, you need disconnect the line first, then make assembly. otherwise it will shows error.
(2) Assembly will not work for "Auxiliary Graphics".