Argonite is a type of sand that uses crushed coral I believe. Live sand is sand with living things in it, like bacteria, bristle worms, and other creatures. If you don't buy live sand, it will become live eventually as your tank matures. The life in the sand helps filter the water. Buying 'live' sand as you see it at the store can help speed up the process of seeding the the sand bed with life thereby shortening the cycling period. I don't know how much it helps to buy it already live though. I bought live sand for my nano and it seemed to cycle faster, but other factors could be involved.
Oh yes, there is no such thing as a dumb question here or anywhere.
Mike