These commands work on objects selected with the Transform Tool (arrow) or in Objects Inspector.
There is tutorial on how to use shaping commands as mask for splitting objects available here.

The main menu > Transform > Shaping commands allow to modify and combine selected objects with use of the Boolean operations like Union, Intersection and Difference. They work only with the solid objects of fill, sfumato and column type. These commands do not work with outlines, manual stitches and connections. To use these commands, select several objects.

Embird Studio - Shaping

Two selected objects - star and rectangle. Star has an opening.

Union - this command creates an object or objects that contain all selected objects merged together. Vertices inside of the filled areas are erased. If selected objects do not overlap one another, result of the union are copies of the original objects.

Note: this command can be used to create underlay (fill without cover stitches) under the whole design, for example. Select all objects and use the Union command to merge objects. Then open Parameters window and set underlay parameters. Uncheck the Make Cover Stitches box to eliminate the top stitches and leave underlay only.

Embird Studio - Shaping

Union of two objects.

Intersection - this command creates an object or several objects that are intersections of the selected objects. If selected objects do not overlap one another, this function does not produce any new object (as intersection does not exist).

Embird Studio - Shaping

Intersection of two objects.

Difference - this command subtracts selected objects from the object that is first in order of creation among the selected objects. It is necessary to arrange order of respective objects in the object inspector list before use of this function, to assure proper order of objects. Newly created object or objects contain only those areas of the first object that are not covered by the next objects.

Embird Studio - Shaping

Difference of two objects.