The term "content" refers to the information and active functionality of a Web site.
All sites provide information of one sort or another, whether that information is purely functional (like a train timetable), intended for entertainment (like a story or a humourous article), or somewhere in between (like a cake recipe, which although it has function is also likely to provide enjoyment).
Some Web sites are active, as well as simply providing information. For example, ecommerce sites allow users to place orders for goods, and many sites include a forum area where visitors can contribute to discussions about the site or its subject. Charity sites allow people to donate to their cause. Sites for musicians might allow musicians to upload their works, and allow others to offer positive criticism.
Deciding on content
You probably have a good idea of the basic content that will be included on your page. But, in order to create a good Web site, you should consider carefully what people will want in case there is useful content that you didn't think of initially.
Content should be organised according to a clear structure which users can understand.