To Create an Assembly Feature
1. Open or activate an assembly.
2. Select a feature from the Datum or Cut & Surface groups.
3. Define the feature. These may be:
Pipe and cosmetic features
Features that remove material
Datum features
* 
When you create assembly datum curves at the intersection of surfaces, you must select assembly surfaces or features. You cannot reference part surfaces.
User-defined features that do not add material
Internal volume features or enclosure volume features