What does this graph mean?

There are two lines on the graph which show cumulative cost over time. The brown line is what you're currently paying. It represents you paying some amount every period, and the total amount of money you will have paid keeps increasing. The blue line is the graph that shows what happens if you do your own. When the brown line is underneath the blue line, you've spent more than you needed to. When the brown line is above the blue line, that means it's cheaper from then on to make your own. So if the breakeven point is 10 coffees, then as long as you buy less than 10 coffees, it's cheaper than making your own. If you buy 11 coffees, it would have been cheaper to make your own.