How Facebook is in an online social networking industry and for the product and service it produces, you can mention how Facebook allows users to interact with others such as friends and family (for personal life) since it is a social media site, and it also allows companies to promote their product or service (by having company pages, sponsored advertisements, etc)
You can also mention about how the advertisements work for this part too. ALSO, WHEN YOU DONE THE SUMMARY,PLEASE PROVIDE ME THE " REFERENCE".