The textbook shows us 'typical' cost curves and we now know (from our first case discussion) that actual shapes may vary by industry as shapes are driven by technology (or engineering). We have also seen that 'data' can come in different forms - a spreadsheet for example or as in this case an equation for total cost, from which we can derive average and marginal costs and plot the function.
This is for a power plant. And it is an engineering cost function since I was told it's from the design manual. So we see declining average costs (at all levels of output) which makes this like a 'natural monopoly' and we also see the marginal is below the average, since the average is declining.