Although you can access this form from multiple sources including J3SG, Rank & Filed, and SEC.gov, this site goes straight to the heart of the matter. Form 4 is filed every time an insider’s stock position changes through an acquisition (usually through a purchase or grant) or a disposition (usually through a sale of stock or a gift of stock). By reading the most recent Form 4 filed by an insider, you can usually get a full picture of his or her current position in directly and indirectly held stock. The footnotes will tell you who are the legal owners of the indirectly held stock, if any.
Form 4 will distinguish between types of stock the insider owns. See example. The most common types are “common stock” (ordinary stock that anyone can purchase and own) and “derivatives”. The most common type of derivative is a stock option: the right to purchase stock at a set price (the “strike price”). When the current market price of the stock is above the strike price, the stock is “in the money” and is a good deal for the insider. When the market price is below the strike price, the stock is “underwater” and there is little reason for the insider to exercise the option. The strike price of each batch of options granted to the insider will be listed on Form 4.
Always read the footnotes to learn whatever they reveal about the nature of the securities involved and the insider’s relationship to them.