I'll try to put it in perspective for you. When the fermentation is complete, it means the yeast has consumed all the sugars it can digest; however, there may still be some sugar in the wine that your yeast couldn't eat. You therefore have to protect or stabilize your wine from any wild yeast ( they are in the air everywhere) that might be strong enough to eat that remaining sugar and start fermenting again, something you don't want. Also if you add sugar later to sweeten, any remaining yeast might snack on that as well.
To stabilize you should add some sulphites - this can be either sodium or potassium metabisulphite; they are more or less the same for this purpose. Campden tablets are just the same thing, generally potassium metabisulphite ( aka Kmeta or sulphite/sulfite) in tablet form. This sulphite stuns any viable yeast when you add it. It also can kill any other little nasties and will also protect your wine from oxidizing when it is exposed to air so it's a very important thing to add.
Potassium sorbate ( aka sorbate) also stabilizes by preventing any viable yeast from reproducing ( think birth control for yeast) and yeast needs to reproduce to ferment.
Thus by adding both sulphite and sorbate you pretty well ruin any chance some yeast has of restarting fermentation - your wine is now stable.
Conditioner is normally just a sugar syrup pack to sweeten your wine - it has some sorbate in it but this is just to protect the conditioner itself and will not protect your wine.
If you want to sweeten your wine it is done after it has been stabilized - this is referred to as back sweetening.- Most people use the conditioner or make a simple syrup by dissolving table sugar in boiling water and this can be added to taste.
Sorry to be long winded, but I think it is easier if you understand the process.
