The primary network (X, P, and C-chain) is a permissionless network. This means that anyone can build on the Avalanche® network.
Avalanche also enables the creation of both permissionless and permissioned Subnets. Anyone can use the AVAX token and launch a new subnet or validate an existing permissionless Subnet. However, private deployments on Avalanche will remain permissioned. This hybrid architecture is what enables Avalanche to seamlessly connect all Subnets together while giving the end-user complete control over his/her subnet.
To learn more about Subnets please read the following article.