The earliest writings in Chinese, which can be traced back 3500 years, were pictures carved on oracle bones. They are known as pictographs. Over the years they developed into characters which are formed of brush or pen strokes. Altogether, there are about 50,000 characters. In 1950s and 60s, China went through the language reform movement and 2000 characters were simplified. These are known as 'simplified characters' as opposed to 'complex characters' (also known as 'traditional form'). All the characters introduced here are simplified characters.
You need around 2000 characters to be able to read and write.