Discord.Net/docs/guides/samples/first-steps.cs

using Discord;
using Discord.WebSocket;

class Program
{
    // Convert our sync-main to an async main method
    static void Main(string[] args) => new Program().Run().GetAwaiter().GetResult();

    // Create a DiscordClient with WebSocket support
    private DiscordSocketClient client;

    public async Task Run()
    {
        client = new DiscordSocketClient();
        
        // Place the token of your bot account here
        string token = "aaabbbccc";

        // Hook into the MessageReceived event on DiscordSocketClient
        client.MessageReceived += async (message) =>
        {   // Check to see if the Message Content is "!ping"
            if (message.Content == "!ping")
                // Send 'pong' back to the channel the message was sent in
                await message.Channel.SendMessageAsync("pong");
        };

        // Configure the client to use a Bot token, and use our token
        await client.LoginAsync(TokenType.Bot, token);
        // Connect the client to Discord's gateway
        await client.ConnectAsync();

        // Block this task until the program is exited.
        await Task.Delay(-1);
    }
}