It's a kind of board game without board (= tabletop game), where two players bring their own, personally optimized armies to fight a battle. The armies consist of small miniatures, which are either made of plastic or of tin (depends on the miniature, it's a technical question, I don't see any pattern when tin and when plastic is used). You buy them for a shitload of money, and you colour them yourself as good as you can, and then you create an army following certain rules of the corresponding "Armybook", that tells you everything you need to know about collecting and playing one of the over a dozen armies. Then you fight, following some clearly defined rules, turn-wise, and using dices (d6) to fight and decide anything which can have different outcomes.
Armies look like this:
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login(Those are the Tomb Kings of Khemri, oviously an undead army with Egyptian theme, fighting against the Skavens, the rat-humans. The first, rather "brown" line of miniatures of this picture are the Skavens)
And this is how one of the troop types is listed in the armybook:
visitors can't see pics , please
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loginAs you can see, the unit size is between 10-40, so you have to at least buy 10 skeletons for your army, which means you are buying unit-wise. This is standard, unless you buy some special things like Necromancers, Bone Giants or chariots, they usually come as single modles for obvious reasons.
(In this game you simply assume every model owns a one handed melee weapon, be it a dagger, sword, axe or mace. That's why the first option says you can switch the bow for a shield, which sounds awkward if you don't know the game
Edit: oh, I just see it's shown in the "Weapons & Armour"-line that they have a hand weapon)