An example
Let's say that I want to determine the percentage of Best Buy's (BBY +1.47%) authorized shares that had been issued as of the end of the 2015 fiscal year. Looking at Best Buy's 2015 annual report, I can find the balance sheet in the financial statements section of the report. In the stockholders' equity section, the company says that it is authorized for up to 1,000,000,000 shares and has issued 351,468,000 of these. Based on this information, we can see that Best Buy has issued 35.1% of its authorized shares.
Percentage issued = (351,468,000 / 1,000,000,000) × 100 = 35.1%