Computers are powerful tools for creation. You can use a computer to write stories, draw pictures, take photographs, record music, and capture video.
When you draw a picture, only one copy exists. You can keep that copy, or give it to a friend, or maybe even sell it.
But when you draw a picture on your computer, it is possible to create a perfect copy of that picture. You can keep your picture and give a copy to your friend and even sell a copy, if you like.
Once someone has one copy of your picture, they have the ability to make more exact copies and then share them. They also have the ability to make changes to your picture, and share that. But what if you don't want them to?