Note: Datum planes are created using the Environment / Plane function.
The part shown below consists of three individual solid objects. A diagonal plane was created.
Required Step 1 
Select one or more objects (open or closed) to be cut. In this case, all three solid objects are selected. Press exit when all objects are selected.
Required Step 2
Select the cutting tool, in this case the plane. Only one plane can be selected.
A blue arrow appears on the plane. The arrow direction indicates the side that will be cut. You can flip the direction by clicking the arrow.
Press OK 
or Apply 
in the Feature
Guide to complete the function.
The objects are now cut.
In Side view, you can see how the plane cut the objects.
When completed, the Cut appears in the Feature Tree as follows:
