In OpenBridge Modeler CONNECT Edition at the section sheet you work on a drawing model, not at the model itself. So, the options in the Drawing Ribbon Group like Model Annotation, Place Civil Label, and Element Annotation are not available. Therefore, to add your notes with leaders and text, you need to go to the Ribbon Group Placement and use the option Place Note inside the button Text, as shown in the screenshot below.
Much more information can be found at the video in the link below at OBM YouTube Channel and inside our training materials and sessions at LEARN.
https://www.youtube.com/watch?v=x2l_qxJK0ig