At a certain point in any startup venture, labor IS capital. The entrepeneur might not have the money, but the work they put in will at least get things going. To use your example of a lemonade stand: The enterpeneur could go out, cut down a tree and produce lumber from it. There's the wood to build the stand. They could go out and pick the lemons. They could go out and learn glass blowing to produce pitchers from sand. They could purify the water, etc., etc., ad nauseum. This would work, but it would be terribly inefficient.
They talk of bartering. Money is an indirect barter. You barter your time and effort to produce a good for someone to purchase for an agreed upon amount of money. then you barter your money to someone else for the good they produce for an agreed upon amount of money.