By default, when simply running
openethereum, OpenEthereum will connect to the Ethereum Mainnet. In order to run a different chain, OpenEthereum has to be run with the
--chain option or with a config file specifying
chain = "path" under
[parity]. There are a few named presets that can be selected from or a custom JSON spec file can be supplied.
OpenEthereum supports private chain and private network configuration via Chain specification files provided with
--chain. In addition to the usual Proof of Work Chains, OpenEthereum also includes Proof of Authority Chains which do not require mining. More details on the available options can be found on the Pluggable Consensus page. See also the Demo PoA Tutorial.
Last but not least, have a look at the JSONRPC Guide.