Basically money invested to build a business .. new and continuing. The owner invests the original capital to buy or lease the necessary property to commence business operations. A building, leasehold improvements, equipment, vehicles and funds to purchase inventory and supplies.
On a balance sheet all but the supplies are Assets. (supplies would be expensed upon opening the business). Liabilities on the balance sheet would be any loans he obtained to finance the purchase of any of the assets. The Capital portion of the balance sheet consists of the owners investment, original and continuing.