Set up your service, non-inventory part, and other charge items to track the expenses you incur when you pay for them and the income you receive when you sell them. This lets you keep tabs on the profitability of the items — for example, you'll be able to prepare reports that compare income against expenses for each item.
QuickBooks automatically fills in the description each time you enter a sales or purchase. You can change the description at that time if you want (your change affects only that transaction, not the item itself).