Cookies are special fragments of website that are often left in a browser allowing the web to identify certain browsers. Naturally, analytics and tech geniuses can use these cookies to track you back to your computer. They do this by looking at a number of different things.
This allows them to find out how many first time visitors that a site has received, plus, how many times a visitor returns to the website as well as the original source of the visitors return and the time that the visitors spend on a specific site. This really helps tailor web development into a more viewer oriented platform that helps to increase traffic.
How many first-time visitors a site has received How many times a visitor returns to a website The original source of return visitors How much time has passed between visits