Title says it all.
HOW DO I MAKE A CONSOLE COMMAND
and how do i use it

Take a look at any of the existing plugins. Simply open docs and use universal commands, they are both chat and console

I know but sometimes it won't work and I don't know what to type at some times

What exactly do you have so far?

I tried using [ConsoleCommand("bla")] But when I tried to execute it, nothing happened.

Because you're most likely using the wrong plugin type or method signature. Follow the documentation for universal commands or [ConsoleCommand] and plugin type as RustPlugin, and arguments ConsoleSystem.Arg. For universal command [Command] and CovalencePlugin as your plugin type, args IPlayer, string, string[]

Makes sense, thanks for the help.