Adding section in configuration file?

Hey all! I need to know how to add a section into a configuration file! Heres my code, any help is appreciated.

Code:

class Parkour : RustPlugin
    {
        private Configuration config;
        class Configuration
        {
            [JsonProperty("StartPosX")]
            public float StartPosX;
            [JsonProperty("StartPosY")]
            public float StartPosY;
            [JsonProperty("StartPosZ")]
            public float StartPosZ;
            [JsonProperty("JoinMessage")]
            public string JoinMessage;
            [JsonProperty("WelcomeMessage")]
            public string WelcomeMessage;
            [JsonProperty("TryAgainMessage")]
            public string TryAgainMessage;
            [JsonProperty("LeaveMessage")]
            public string LeaveMessage;
            public static Configuration DefaultConfig()
            {
                return new Configuration()
                {
                    StartPosX = 0f,
                    StartPosY = 0f,
                    StartPosZ = 0f,
                    JoinMessage = "Joining",
                    WelcomeMessage = "Welcome",
                    TryAgainMessage = "Try Again!",
                    LeaveMessage = "Leaving"
                };
            }
        }