The dots are the rows of the table: with one barber the shop produces 16 haircuts at a total cost of $240, with two barbers 40 haircuts for $320, and so on up to six barbers and 84 haircuts for $640. At zero output the fixed cost of $160 is still there, which is why the curve starts at $160 on the vertical axis rather than at zero. That intercept is bracketed as the fixed cost.
Once production starts, variable costs are added. At first total cost rises at a decreasing rate, because a second barber allows specialization and each barber adds a lot of output. Then diminishing marginal productivity sets in and the curve bends upward: each extra barber adds fewer haircuts, so each extra haircut costs more. The sliders change the fixed cost and the daily wage.