Please tell me, i have seen them mentiond in many threads and a i know they are some sort of musket infantry, but really what are they exactly?

An arquebus was a very early and primitive form of firearm that tried to deal with the shock of firing them (the recoil) by having a metal rest on the barrel for resting the gun on a wall or fence when firing. Remember that the earliest firearms were really just hand-held cannons. The Germans invented the arquebus (Hakenbüchse). Later versions of the arquebus devolved down to having a folding metal stand, like a camera tripod, that helped balance while firing as well as absorb the shock. They were used well into the 17th century, although their hayday was in the 15th and 16th.

It is quite common in armies for names to stick long after the technology that spawned them goes out of style so arquebusiers were around much longer than arquebuses were, just like the British and Americans still refer to their firearms practicing drills as "musketry".

I have a related question that maybe someone can answer. Did arquebuses have matchlocks or wheellocks? The earliest firearms were matchlocks, but wheellocks came into being while the arquebus was still being used.

They where match locks, the arquebus also has historical signifigance in Canada, the first French fur traders used them and traded them extensively, infact I think the Civ3 musket man has an arequebus, especially from the armour and helmet he's wearing which seem very French or Spanish and was popular during the time this firearm was in use.

its an early gun.