The Internet started out as a communication device between government researchers, built to share their knowledge. As it developed, more countries used it, it became more comercialized, it became faster, and more portable.
The first computer connected in some way to the internet was the UNIVAC, it was large, and couldn't be transported, so the sending of information became traveling with magnetc computer tapes or sending them through the postal service.
The internet's birthday is considered January 1st, 1983. Prior to this date, various computer networks didn't have a stadardized way to communicate, to fix this, a protocol called Internetwork Protocol or IP adresses were formed to tell messsages sent through the internet, who sent it and where it's going.