Financing activities are all cash-generating activities which take place between a company and its investors.
A company's investors include both its shareholders and creditors. This means that financing activities not only include the issue of stock, dividend payments, and stock buy-backs, but also the taking-on of new debt and the repayment of old debt.
A company decides to issue new common stock. The issue of this stock is a financing activity, as the buyers of the stock are giving the company money in exchange for the promise of increasing future returns.