A Teaching Assistant (TA) will help facilitate conversation in the course. Direct your course content-related questions to the TA if falling behind has caused some confusion.
That said, TAs are able to participate in the current discussion only. If the current discussion is Week Three but you missed Week Two, you will want to seek out your TA in Week Three. Also, rather than addressing Week Two concepts in Week Three's discussion, please post about Week Three, the current lesson. If you fall behind in posting to a specific discussion you still will have access to it to read it and find information.
The course material will not be accessible after the publicized end date of the course, so please pace yourself as to get the full experience of the course. A great way to plan ahead is to look at the course dates at the top of each module / new lesson. See the article Seeing Your Course In Its Entirety for more information.
Date ranges are listed at the top of each module to help pace you through the course. Click on Home or Module to get this view: