Asking for advice

Asking for advice I have a new friend who stutters. It comes and goes with nervousness i think. Sometimes he gets really stuck (apologies if that's not the right term). I dont know what to do in these moments. I dont want to interject but if he's really stuck does that allow him to move on? I feel bad for just standing there looking at him while he struggles. What is the proper etiquette in these types of situations? I want him to be comfortable and not do the wrong thing.