A method is just a class function.

No idea why a new term was needed... nobody really cares if you say function or method really... Technically, since C# is a fully object oriented language, that means everything lives inside a class -> every function is a method.

Defining a method

You do it just as you would do a function, except it within the scope of the class.

class ExampleClass
{
	//empty constructor
	public ExampleClass() { }
	
	public ExampleMethod()
	{ 
		//do something
	}
}

Invoking a method

You do is just as you would do a function, except you have to go through an instance of your class to reach it

class Program
{
	public void main()
	{
		ExampleClass ex = new ExampleClass();
		ex.ExampleMethod();
	}
}