Operations

The Operations menu holds the commands for working with figures and geometries.
To create complex figures, you can use the Combine operation to make up a figure consisting of several geometries.
This operation can be reversed by the Separate command which splits a complex figure into separate geometries.
The Join operation lets you merge the segments with coinciding endpoints into one geometry, and also form a closed figure by merging separate segments of its contour.

The Combine operation is a special case of grouping: it is applied only to figures, and it groups them into a complex figure with a unified line and fill formatting of all its geometries.

If you want to make up a complex figure by grouping several figures that have the same properties (fill color, line color, line thickness, etc.), select these figures and use the Combine operation: menu Shape / Operations / Combine.
When the properties of the figures are the same, it is better to Combine them rather than Group: combined figures take up less space when saved.

If overlapping figures are combined, the overlapping areas become transparent. This feature is extremely useful for creating "holes" in the closed figures.

Note:  If you combine figures having different line and fill properties, all the elements will be formatted after the primary selected figure.

Merge
The Merge operation (menu  Operations / Merge ) lets you merge several selected figures into one. All the shapes take a unified formatting after the primary selected figure.
The essential difference from the Combine operation is that if a solid path results after the operation, it becomes a single geometry. So when several geometries have some coinciding endpoints, the Merge operation merges them into one geometry. (The Combine operation just groups figures with the same properties, but never merges them.) That is why when a closed figure results after the Merge operation, it is filled automatically (this never happens when the figures are combined). below is the showing:

Before merge:

After merge:

Dismantle
The Separate operation (Operations / Dismantle) lets you split a complex figure into separate geometries,
so it is inverse to the Combine operation. If a figure consists of several geometries, the Dismantle operation will form a separate shape for each geometry of the figure. It looks like dividing a figure into parts it consists of. This operation will dismantle the combine shape to children shapes, below is the showing:

Before dismantle

After dismantle:

Intersect
This operation will merge the selection shapes by using their intersect area, below is the showing:

Before intersect

After intersect

Subtract
This operation will merge the selection shapes by using their Subtract area, below is the showing:

Before Subtract

After Subtract