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

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

// Create a module with the 'sample' prefix
[Group("sample")]
public class SampleModule : 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 from")]
		SocketUser user = null)
	{
		var userInfo = user ?? Context.Client.CurrentUser;
		await ReplyAsync($"{userInfo.Username}#{userInfo.Discriminator}");
	}
}