Refer to the API documentation at http://www.multichain.com/developers/json-rpc-api/ for details of the calls.
Example:
internal async Task DoMagic()
{
// connect to the client...
var client = new MultiChainClient("192.168.40.130", 50001, false,
"rpc_username", "rpc_password", "the_chain_name");
// get some info back...
var info = await client.GetInfoAsync();
Console.WriteLine("Chain: {0}, difficulty: {1}", info.Result.ChainName, info.Result.Difficulty);
}