The silkworm makes a cocoon around itself while it changes into an adult moth. The cocoon is made of long threads of silk.
The moth tears the silk cocoon open when it emerges as an adult, which causes damage to the cocoon to stop the adult moth from breaking it. The long threads are then woven into strands.
The Chinese were the first people to use these strands many centuries ago to make silk. For many generations the Chinese kept the secret of silk to themselves. They traveled to the great markets in Syria and traded their beautiful fabrics for Western goods. About 1200 years ago, two monks visited China. They risked their lives to steal some mulberry seeds and some silkworm eggs to take back to Europe.
The technology of how to make silk using silkworm was no longer a secret. However, not many countries could use the technology. For example, the silkworm did not like the English weather! China is still one of the major producers of silk.