Originally Posted by: tanhongzhi

When I play the melody, there are notes, especially open string that keeps ringing even when I don't play them. This causes a lot of unwanted noise.

I cover muting (&the basics of mechanics of physical technique) for beginners in this tutorial.

https://www.guitartricks.com/lesson.php?input=11079&s_id=605

And this tutorial has some extra material on muting that might be beneficial.

https://www.guitartricks.com/tutorial.php?input=2281

Hope that helps!