Glogster is an online tool that allows users to create digital posters called "glogs." Glogs can include text, images, videos, and other multimedia elements. To create a glog, users register for a free account and then add elements like backgrounds, graphics, images and text using the provided tools. Glogs can be kept private or shared publicly by copying the glog's unique URL. Users are referred to as "gloggers" when creating and sharing their glogs online.