I use the Kadee # 5 couplers and the #321 in track delayed uncoupling magnet.  They are delayed couplers which means that once they become uncoupled, it is possible to still push the cars about the track without re-coupling them.  This is really useful as I want to be able to push the cars I uncouple into certain positions.  There are rather simple to use in principle, however in real application there are some challenges.  There are several steps to coupling and uncoupling a car from the train.  The trains start in an uncoupled position as shown in the photo below.  These couplers are in a natural state here.  That is to say, they are not effected by a magnet.  
When these two couplers meet, they will lock together.  The two hook like segments will link up and hold the trains together.
Notice the springs, these hold the couplers in this position.  They will also force the couplers back into this position when the magnet opens them up.  This is actually the next step.  The train must move so the couplers are directly over a magnet.  The magnet will pull the couplers to the open position by pulling the trip pin to the side.  

This will compress the springs and force the couplers to open up.  
As you can see, the hooked sections are no longer overlapping.  At this point the train can pull away and leave the car behind.  However, these couplers have a delayed feature which allows the cars to be pushed without re-coupling back up.

At this point, the couplers are in an uncoupled delayed position.  If the train backs the two cars together, they will not re-couple.  The two strait pieces (one circled above) will prevent the hooks from catching each other like so. 
 
When the couplers are moved off the magnet and the train cars separate, the couplers will revert back to their original position which allows the cars to couple by simple backing one into the other.

     In order to get these couplers to work properly, they need to be calibrated in a sense to the track and each other.  The trip pin should be bent in such a way that it barely clears the magnet in the track.  The couplers also need to be the same height as each other.  This way, they will line up with one another.  Also putting some sort of lubricant in the moving parts of the couplers, both where they connect to the car and in the hook, seemed to help as well.