Dividends (also called Distributions) are the most common way of providing a return for the investment shareholders have made in the firm. Often a firm will establish a habit of paying out a certain proportion of the previous period's earnings as a dividend, while retaining the remainder to invest in increasing the firm's future earnings. The proportion of earnings retained for investment will depend on the firm's growth prospects. A mature firm in a mature industry will often return a very high proportion of its earnings as a dividend because there few growth opportunities.
You may assume that the presence of dividend imputation means that there is no effective tax on dividends (nor any tax on capital gains) for personal investors.