The Primary Network validates Avalanche's built-in blockchains: Platform Chain, Exchange Chain, and Contracts Chain. All members of all Subnets must also be a member of the Primary Network. In order to become a member of the Primary Network, one must stake some AVAX tokens.

For additional information bout Subnets please read the following article.

For any additional questions, please visit our knowledge base or contact a support team member via the chat button at support.avax.network.