Social content sites allow you to upload and share things of interest to you so that you can access them from anywhere that has Internet access.
You could upload photographs, such as a family holiday, and share these with friends and family all over the world. You can add information to your photographs so that when people look at them they can move their mouse over a particular area of the photograph to get more information about it.
You could also upload small videos that you have created. The videos uploaded will typically for good enough quality for delivery in a web browser yet still be small enough to be streamed over the Internet. If you wanted to uploaded higher definition videos you would generally have to make a payment for a premium account.