break-even point is when the sales match your costs, so if you spent $100 on the products and you sell $100 at some point, that's your break-even point, your cost are covered, well no profits but no losses either. Well, that happens when obviously enough R(x) = C(x)

profit is surplus from your costs, so, so long your sales exceed your costs, whatever is over the costs, is your Profit, so not so oddly enough Profits is the difference from revenue and costs, namely R(x) - C(x).
