Union is one of the three Boolean functions in Shapr3D. As its name suggests, you can use the tool to unite bodies and groups.
You may find the tool useful when you want to reduce the number of bodies you need to select. The tool is straightforward:
- Go to Menu > Tools > Union.
- Select each body you want to unite.
- Turn on the Keep originals switch if you want to keep the original, separate bodies.
If you only need the new, merged body, then turn it off.
- Select Done.
You can double-check if your bodies are actually united by selecting one area of the union. The entire union should be selected.
💡Shortcut💡: If you select all bodies that need to be united first, the menu is customized automatically. From this adaptive menu, go to Union. 
This tutorial can show you how the tool can be used: