Every word is made up of symbols or characters. When you press a key on a keyboard, a number is generated that represents the symbol for that key. This is called a character code. A complete collection of characters is a character set.
Different languages use different keyboard layouts. For example, a French keyboard has an é. If we were writing in Japanese or Arabic, we would need even more choices of characters.
In theory, anyone can create a character set. But it is important that computers can communicate so we use global standards for character sets.
You can check what character encoding your web browser is using by looking in your browser settings: