Like everyone else says, I think you are a great sister for being there for him. Or brother, not sure if you specified. Anyways, I think the most fundamental thing you can do to help him, for *starters*, is be there for him in a conversation. Show him that the words he says are understood and they can affect the way you feel. Be as present as you can. A stutterer has a harder time communicating to someone who doesn’t appear to be listening. Another thing, you should encourage him to gain confidence in other areas unrelated to speech. His fitness, finances, clothing, his vehicle if he has one, clean his living area, improving his skills related to hobbies, etc. Stuttering is a highly mental struggle and it is incredibly uplifting for a stutterer to have all of the other areas in their life squared away. Another thing, the most important for me, it might be hard to incorporate into his life just by talking to him, but he should try meditation. I made a post about this on my page, check it out if you want. Meditation has been so helpful for me.