Total cost is the sum of fixed costs and variable costs, and can be expressed as functions like C = a + bx or C = ax^2 + bx + c, where C is total cost and x is quantity. Profit is calculated as total revenue minus total costs, so the profit function is P = R - C, where R is total revenue and C is total costs. The break-even point is where total revenue equals total costs so that profit is zero, or R = C.