A map of Atheus:
To mix science with fantasy, the tectonic plate that Atheus lies on is cupped by another. This makes a convergent fault lines on the western side of Atheus, and a transform fault line on the south edge. For those unschooled in geology, that means that the western side will have volcanoes, earthquakes, and tsunamis, and the southern side will have earthquakes and tsunamis. This makes the northwestern islands volcanic islands.
Magic stems from a being's life force (LF). To use a spell, one must tap into that LF. Your LF can be considered your soul, mana, whatever is more comfortable for you. Because magic stems from your LF, all magic, be it through spells or magic, display your aura, which is a color or pattern that represents who you are. For example, a violent person might have a red aura, a passionate person might have a pink one, a necromancer might have black skulls, etc. For warriors, my How Weapons Become Magic Weapons sub applies.
Humans: standard. Same as actual humans. Generally distrustful of other races, and view them as barbaric. Less attuned to magic than the other races, they make up for it with superior technology (but they are not steampunk- still medieval technology). The humans also have the highest birth rate of all the humanoids (except goblins), and thus were able to push the other races out of their eastern portion of the map (see history).
Elves: picture magic wielding Native Americans. The elves are a down-to-earth folk, and don't bother with fancy metal weapons. They can usually do with wooden spears, perhaps tipped with a sharp rock or bone, and wooden bows. But since they are very attuned to magic, such weapons can be deadly. They are most known for the more natural magics, and can survive in most any environment. Though they love the environment (and all habitats, not just forests), they understand about Survival of the Fittest, and they intend to be among the Fit. They are fully capable of taking lives, be it animal or humanoid. These are not vegetarians.
Dwarves: sturdy, stoic folk, they are more attuned to magic than humans, but typically use it in crafting and wars. These folk hold grudges like no other. They do use metals, unlike the elves, but need to acquire the metal ores itself and forge them, which makes having actual metal items a rarity among dwarves. Usually only chiefs and upper-clan member have metal weapons. The rest make do with whatever is easy to construct with whatever's at their disposal- wood, stone, bone, etc.
Goblins: smaller and weaker than all of the other races, they make up for it by being, on the whole, smarter and higher birth rates. Though they can use magic, they typically can only make magic items with it- which the other races can also not do (the enchantments are permanent and apply for all, unlike the natural process in the sub linked in the magic section). Because of this ability, many races come to them to enchant their weapons. They will use whatever weapons they can find, whether they make it of wood, or salvage it off the corpse they just killed. The goblins can also, very rarely, produce the Hobgoblin, which is a bigger, stronger, and more powerful goblin. The Hobgoblins can use whatever magic they can easily and are as powerful as, perhaps, 1.5 humans (as an abstract scale). Of course, this means that they are about 3 goblins in a flat-out duel (and the 3 goblins can't use tactics).
Orcs: the orcs are the barbarians of the barbarians. They have a complete lack of magic, but are stronger, and bigger, than all the other races. Their culture's main feature is violence. If you have never killed, then you are a child, no matter if you are young and fresh or old and wizened. No female would consider a male as a husband if the male has never killed, and view the more kills as the better a "Catch." A general rule of thumb is the more kills a warrior has, the more wives he has in his harem. Therefore, the orcs stay in a state of near-constant war. Also, eating vegetables is seen as week. Meat is the primary course on the table for dinner, with perhaps some vegetable on the side or on the meat. Since killing is the tenet of their culture, killing of animals is seen as better than picking of plants. Another major feature of their society is honor and duty. Though they do wage wars continuously, if you manage to befriend and orcish tribe, they will never attack you. That is, the current leader will never attack. The next one might, and probably will. Also, orcs produce litters of babies instead of a single baby per pregnancy. There will typically be around five babies per litter. One of these babies will usually be a runt. These runts are known as kobolds. The kobolds lack a place in orcish society, and will usually get the least of everything. In times of starvation, the orcs will send off the kobolds first. Because they are smaller and weak than the rest, the kobolds typically to the unhonorable jobs. It is common to have koboldian archers in an orcish attack.
Each of the sentient races has their own language, except for the humans, who have two. However, there are many different dialects for Elven, Dwarven, Goblin, and Orcish, which tends to run on a north-south axis. A dialect 60 miles north will be more obscure than a dialect 60 miles east.
The humans, however, have two. A Low Tongue and a Old Tongue. The Low Tongue is for everyday conversations and for commoners. Its used when someone's off to the market for more bread, when kids are off playing, when teens are funneling off angst, etc. The Old Tongue is the root tongue of all the other languages, like Latin is for French, Spanish, and all the other Romance languages.
The Low Tongue is typically taught to the barbarians, as its used as a go-between for the various tribes. However, some tribes don't teach it to their young, for reasons of their own. These may run from hatred of the humans to such a degree that they won't use their language, to to busy killing other people to bother talking with them (a trait common with the orcs).