Mobile:
Go to Work Orders tab
Select Work Order to use Part
Click Edit in top right corner
Click Add Parts in Parts Needed field
Select Part(s) to use
Enter Amount needed per Part
Click Done in top right corner
Click Update in top right corner
Web:
Go to Work Orders tab
Select Work Order to add Part
Click Edit in top right corner
Select Part(s) to use in Parts field
Enter Amount needed per Part
Click Update in bottom right corner