Your introduction will serve 3 purposes: to introduce the topic to your students, to establish yourself as the teacher/author, and to outline the structure of the module.
Creating an online module means that you have to be very conscious of building trust – the most important commodity in teaching and learning. You will only learn from someone you trust. As a SenGuide teacher, your expertise comes from your life experience, from lifelong practice, from studying either formally or informally. In any case, you have a great knowledge of your topic, and your students need to know that.
This is a good place to tell the story of your experience with the topic: write it as text, or write it as a script that you use for a video where your students can see and hear you. Remember, make this description as short and clear as possible and please do not get lost in details. The details should be revealed later in the content of your learning unit.