Calls and puts give the owner the right to buy or sell a stock at a certain price by a certain date. When the holder of a call or put option has an option that is "in-the-money" (i.e. the strike of a call is below the current stock price, or the strike of a put is above the current stock price) and decides to buy or sell the stock, that is known as "exercising" an option.
Options involve risks, including substantial risk of loss and the possibility an investor may lose the entire amount invested in a short period of time. Before an investor begins trading options they should familiarize themselves with the Options Disclosure Document. Tax considerations with options transactions are unique, investors should consult with their tax advisor to understand the impact to their taxes.