Design Animation > Design Animation > Creating an Animation > Defining Bodies > About the Body Definition Dialog Box
  
About the Body Definition Dialog Box
Use the Body Definition dialog box to add parts to a new body.
Name—Enter a name for the new body.
Add parts—Use normal selection methods to select the parts you want to add to the new body. To add a subassembly, select it in the Model Tree.
The Number of parts display box updates incrementally as you add parts to the body.