How do I get the result of a checked checkbox?

I'm really new to HTML, but I can't find anywhere how to return the variable from a check box. I've figured out how to get variables from forms and inputs, but I don't know how to get them from check boxes. Basically, I want a check box that if checked, will return the value yes. If not checked, it doesn't have to return a value, but no would be nice.I'm really new to HTML, but I can't find anywhe