The unidirectional approach to information retrieval on the web is known as Web 1.0. It implies visiting static websites where you can review and download information, but without an effective communication with the owners/creators of the site. One good example of a Web 1.0 tool is the webpage used to request your passport. Usually webpages for registering in universities are Web 1.0.
Web 2.0 implies bi-directional communication. There is more to them than just browsing and downloading. You can post information and obtain immediate responses. Blogs are perhaps the most typical and emblematic of the Web 2.0 tools. Chatting devices are also a good illustration.
Blogs have obvious educational uses. You can design a Tutor blog, where the teacher has control on the contents posted. Or you can have a Class blog, with the participation of both teacher and students. A more encompassing approach is the Learner blog, where all participants are free to post comments on whatever subject of interest, ask or answer questions from the teacher or their classmates alike, etc.