Every business has costs that don't move with sales volume — rent, salaries, software subscriptions — and costs that scale with each unit sold, like materials or payment processing fees. The break-even point is the exact number of units (or the exact revenue figure) where the money coming in from sales finally covers both kinds of costs completely, with nothing left over and nothing short.
Below the break-even point, every sale still loses the business money overall, even if each individual unit is sold at a profit on paper — because the fixed costs haven't been paid off yet. Above it, every additional unit sold drops straight to the bottom line as profit, since the fixed costs are already covered.
Break-even analysis is one of the first things a new business or new product line should calculate, because it turns "will this work?" into a concrete, falsifiable number: a specific sales target to hit, rather than a vague hope.