How do you make Liquid cheese for nachos?

usually when i make nachos i use american cheese and then put it on some plain chips and microwave it. It isn't liquidy at all it's just like it was but melted, completely dry. I ask this because my family adores eating nachos and we usually go to Taco Bell for it because of how good the liquidy cheese are. So what's the best way to make liquidy cheese?