Just like the above poster says. Come up with something that is meaningful to you and say it to yourself either silently or out loud. My personal affirmation starts with 'I enjoy the art of communication, I communicate with confidence and clarity, in the moment, from the mind', I have a couple more lines but you get the gist. Once you start you might add things or change it up as you go, the important thing is just to make a start and see how it feels. You can't do it half hearted, relax and commit to the affirmation, try to 'feel' it. I personally try to 'think' my affirmation in my mind rather than physically saying it out loud. For so many years my attention has been on physically saying the words and I believe that was not the best approach. I can speak fluently when alone and I now put a lot of my problem down to a type of performance anxiety. Not all of course, I am a PWS but in the complex entanglement from years of stuttering I often subconsciously predict a bad outcome before I even speak. I believe affirmations help to re-write my thinking to a more positive mindset and stop my mind from jumping forward to predict problem words while I'm speaking.