Discord.Net/docs/guides/commands/samples/module.cs

// Create a module with no prefix
public class Info : ModuleBase<SocketCommandContext>
{
	// ~say hello -> hello
	[Command("say")]
	[Summary("Echos a message.")]
	public async Task SayAsync([Remainder] [Summary("The text to echo")] string echo)
	{
		// ReplyAsync is a method on ModuleBase
		await ReplyAsync(echo);
	}
}

// Create a module with the 'sample' prefix
[Group("sample")]
public class Sample : ModuleBase<SocketCommandContext>
{
	// ~sample square 20 -> 400
	[Command("square")]
	[Summary("Squares a number.")]
	public async Task SquareAsync([Summary("The number to square.")] int num)
	{
		// We can also access the channel from the Command Context.
		await Context.Channel.SendMessageAsync($"{num}^2 = {Math.Pow(num, 2)}");
	}

	// ~sample userinfo --> foxbot#0282
	// ~sample userinfo @Khionu --> Khionu#8708
	// ~sample userinfo Khionu#8708 --> Khionu#8708
	// ~sample userinfo Khionu --> Khionu#8708
	// ~sample userinfo 96642168176807936 --> Khionu#8708
	// ~sample whois 96642168176807936 --> Khionu#8708
	[Command("userinfo")]
	[Summary("Returns info about the current user, or the user parameter, if one passed.")]
	[Alias("user", "whois")]
	public async Task UserInfoAsync([Summary("The (optional) user to get info for")] SocketUser user = null)
	{
		var userInfo = user ?? Context.Client.CurrentUser;
		await ReplyAsync($"{userInfo.Username}#{userInfo.Discriminator}");
	}
}