When you are browsing the web, individual sites can store cookies on your device. Cookies are small text files that contain data that the website can use when you visit them again. The purpose of these cookies is to make the websites easier to use or to personalise the content for you.
Google store cookies on your computer containing data about searches you have carried out. If (like me) you searched for holidays in Florida, Google could use this to promote these holidays. Google places adverts on lots of websites, not just websites owned by Google so you may encounter personalised adverts on other sites.
Ease of Use
Cookies may recall personal information that you enter such as your username, address and email address to make forms easier to complete on the website. For example, when I book my flights home to Ireland, Ryanair can use this data to complete the booking form making it easier for me to complete the transaction.