Chain providers provide access to an evm on behalf of an API provider. Your Airnode will interact with one or more chain providers and respond to requests. You can use multiple chain providers for each chain and declare multiple chains each with one of more chain providers. Below are some of the chain providers you might use.
In this example, the first (and only) element of the chains array specifies the Sepolia blockchain via the id11155111. The type is set to evm, which is the only type currently supported by Airnode. The providers field specifies a single provider, the name of which is arbitrary and in this case is infuraSepolia. The inner object contains a single url field, the value of which is interpolated from secrets.env.