When you first create your course in the Biling and Shop section, you'll decide how many E-Modules and/or coaching calls you want to include, and when they will be delivered.
When your course starts, your course members will be able to access all the tabs in their course. So that they are not greeted by a blank Sessions page, and to welcome them to the course, you'll create an introductory module. This could be as simple as a welcome message, or it could be the first module you are delivering, with full content. In the section marked Introductory Module, just choose a title and write a short description. You'll be able to create the content for this and all other E-Modules from Course management after the course is created.