A welcome message to students before the course begins is an important step in establishing your online. The message should include vital information for the course and your entire syllabus. The purpose of this communication is to welcome the students, establish a comfortable class environment, introduce the class syllabus, schedule, protocols, and to/or establish a weekly routine.
This is the first opportunity you as the instructor have to address what the course is about. Take this time to briefly describe the goal of the course and to address any common misconceptions. This is an excellent opportunity to address how the course routine (i.e. content will be released each week or the whole course is open from the beginning).