Here you can select from pre-made products/services, which automatically fills in the description and price you previously entered. This is good if you frequently do the same job.
You also can create a new service and add the price and description if you have not yet created any products or services. This can either be in bulk or at an hourly rate.
On the left side to the product/service column, you can change the quantity so the price adds up. This is good to add in estimated hours needed if you're charging by the hour or if you're doing multiple of one thing like unblocking drains.
To the other side of the Product/Service column, you got the description for each product or service. This is where you add a brief explanation of what the service is. This is vital as if there's no description there nothing will appear on the quote, just a price.