Heraldry is science about coat of arms. Since this is presentation of Serbian national marks, it is necessary to say a thing or two about heraldry. There is however no need for further elaboration of this topic (here), since there is plenty of information about heraldry on Internet, (which is not case with Serbian Coat of Arms) and anyone interested can read all about it.
In Middle Ages when knights used to wear helmets and armors, was hard for them to identify each other. Because of that they started to wear marks (coats) of their rulers. Especially during crusades this custom spread across Europe. Soon there were too many different coats so kings couldn't remember all of them. That's why they established heralds. During the battle herald used to stand beside a king to explain him which army belongs to which ruler.
Since XI - XIII century we have the first rules of heraldry. First and the most important is: coat must be cognizable (clear) from distance - it is logical, isn't it. That's why a color mustn't stand beside a color, and metal mustn't stand beside a metal. Metals are gold and silver (yellow and white). Furthermore we use only pure colors, not pastel or mixed, so they can be clear from distance.
"Charge" is what we put inside the coat, usually some animal or plant, but it can also be a castle or anything at all.
If we "describe" the coat properly, every herald could draw nearly the same coat, using our description. There are computer programs that draw coats (more or less effectively). That description is called "blazon". Blazons are quite simple; all you need to learn is terminology, which is combination of French, English and Latin.
Colors names are: yellow (gold) - or, white (silver) - argent, red - gules, blue - azure, black - sable, green - vert, violet - purpure, orange - tenne, sky blue - bleu celeste, "blood" red - sanguine, dark red - murrey...
I would recommend every visitor to view some basic blazons. That keeps heraldry from being boring.