In the operations (PART/OPS) tab, you specify each of the repair operations you are billing for in your RO. There are several built in shortcuts that can make this quick and easy.
In general, you "build" a line by first entering something for Operation by typing or choosing from the drop list (which you can edit). Then, as an option, click or type a Position. (Left, Right Rear etc.) Specify a quantity if necessary.
In the example below. The section for Front Lamps has been clicked on the right (circled in yellow). When the arrow next to PART is clicked, it displays a list of parts for front lamps. Just click to select. The beauty part is that these lists are pre-loaded with many common parts but can ALSO be CUSTOM edited by you, the shop owner! Then enter a part number (optional), price and labor time.

Use the button New Part to add a part to the RO. A line at the top of the tab tells you which part you are working on; in this example it part 1 of 2 parts.
Use the buttons First, Previous, Next and Last to move from one to the next.