just started riding and took the mss course but still a little unsure about somethings.if i am say in 4th gear do i have to downshift every gear before i come to  a complete stop  

I'm sorry, but I would respectfully suggest that you need to take the course again, and pay attention to what your intructors are saying and demonstrating.  Of course you can release the clutch again without shifting gears if it is unnecessary to do so.  However you should try and avoid coasting....stay in gear and under power.

When slowing down you have the option of downshifting and using the compression of your engine to reduce speed and at the same time maintain engine revs at optimum levels in order to ensure you have the power you may need to accelerate out of potentially dangerous situations, but touching the brakes has it's purpose as well.  As long as a brief touch of the brake does the job for you, that's fine too.  An additional benefit to you as a warning to others (bikes or otherwise) travelling behind you...the brake light warns that you perceive a threat ahead or are simply preparing for an impending stop situation.  Nobody is in a position of trying to read your mind.

Riding is a multi-tasking situation in an ever-changing environment, some aspects over which you have no control.  Risk assessment, and the steps necessary to minimize exposure and vulnerability to them, must be at the top of your list of priorities at all times.  The mechanics of it all, the braking, shifting, maintaining rpm's, etc are all a matter of quality instruction, comprehension of how they work in concert with one another, and practice.

Please take the time to get good advice from fellow riders around you who you trust and/or keep in touch with the instructors from your school and go back and ask them the same questions.  I would be shocked if they were unwilling to review the these things with you on a simple conversational basis.

But please exercise caution, and PRACTICE.  I fear that you really do need to, and are unnecessarily risking your well-being by seemingly being more than a little uninformed at this point in your riding life.

Be careful,  Don't become an avoidable statistic and victim.

Sincerely, Herb.  

That was a pretty condescending response.  The mere question does not indicate the rider is a newbie, or didn't pay attention during the course.  Maybe they're only looking for reassurance, and that's what these sites and forums are intended for.  If it's too much trouble to provide a simple answer without the lecture, then don't respond.  

To help with the original question:
When to downshift:
What you need to do is learn your bike.
In each gear, play around and find what is the lowest speed that you get acceptable acceleration. Crank it, and feel where the surge starts... that would be it.
That is the minimum shift point for each gear.
Yes, the bike will still accelerate at slower speeds, but, you're just waiting until you can get some real acceleration. That's dangerous on a vehicle where you are protecting the frame with your body.