Q: How send a message with a Discord Bot in C#? I'm trying to understand how should I send a message with Discord Bot into my channel without any event or command sent by me?
The result that I would like to achieve is that through a timer bot you send a message in the chat every minute.
If you can explain it to me with some examples, I would be very grateful to you

A: There are various ways to send messages into channels without using commands. In essence, you are asking how to send messages from a class that does not inherit from ModuleBase. 
This requires you to use Dependency Injection to inject your DiscordSocketClient into the class you want to send messages from. 
You can learn more about Dependency Injection (because it is a large topic) in the official documentation and in the example bot provided by Discord.Net (assuming you are using this library). 
The simple solution is shown below.
public class MyClass
{
    private readonly DiscordSocketClient _client;
    public MyClass(DiscordSocketClient client) => client = client 

    public async Task SendMessageToChannel(ulong channelId, string message)
    {
        SocketChannel channel = _client.GetChannel(channelId);
        await (channel as IMessageChannel).SendMessageAsync(message);
    }
} 

Ideally you should also create an interface called IMyClass and have MyClass implement it. This way, you can effectively configure the methods of MyClass as a service too. 
