Information gets on the Internet when somebody decides to make it available. For example, a company may put information about products and services it offers; a person may set up a personal Web site with any information he considers worthwhile to share, a non-profit organization may share information it considers important, a political or religious organization may distribute information about its goals, etc.
By the way, the information "on the Internet" is actually stored in hard disks, and similar equipment, on computers called "servers". The Internet is not a place to store information, it is just the way to access that information.