The union Boolean produces a single solid that represents the combination of all stocks and all tools. Stocks and tools are indistinguishable.
Pick both solids (the order is not important). On the Structure ribbon in the Entity Modification group, click Boolean and choose from the drop-down menu. Click to close the Edit Properties dialog box.
The view now displays the result of the union.
Notice that the union has a presence in the Browser under the Geometry node. The cylinder is located under the Creation -> Stocks node and the box is under the Creation -> Tools node.
By default, unnecessary faces and edges are removed from a Union Boolean. To preserve faces and edges of stocks and tools, set the Simplify parameter to False in the Boolean's Edit Properties dialog box.