To add a new part for your equipment go to the the Resource Tab>Trucks/Equipment
Choose the equipment you’re adding the parts for and click the pencil button.
Next click the “Parts” tab.
You will see any parts you’ve added for this equipment here.
Click the green “+ New Part” button to add a new part. 
A pop up will appear for you to add the part number and a description.
When done, click the blue “Save” button.