That's a key question many times everyday. In public address it is key to controlling speaker anxiety (stage fright.) If you know what the goal is and you've explained this others before, and you have a pretty good idea who you're talking to, you've gone a long ways to a less fearful presentation.
Goal: what do I want them to be able to do or think when my presentation is finished?
Practice: I have explained this to others several times and have a pretty good idea of how it should be done.
Audience: I've know this audience pretty well, and I've talked to them in other circumstances before successfully.
Now you've got an excellent start on being ready. That is going to help a great deal when you are standing before them and trying to make sense.