To merge two ploygonal shapes:
1. They must adjoin or overlap.
2. Select one of the two.
3. Make sure the current tool is the same as the selected element.
4. Click the edge or a node of the selected element and choose the add (+) option on the pet palette.
5. Space bar click (magic wand) in the area or on the edge of the other element.
6. Select and delete the second element.
It's not a quick as a merge function could be but it is more versatile as it can work on dissimilar elements.
