If you have ever eaten a wine grape by mistake, you would have figured out very quickly that they are not the same as your normal table grapes. But unless you happen to live next door to a vineyard, it is pretty unlikely that you stumbled upon (and then went ahead and ate) a wine grape.
So. What's the difference?
Well, table grapes have been selectively bred over many generations to make them more appealing to eat whole. Their skins are thinner, their seeds are smaller, they are bigger, and not as overpoweringly sweet as a wine grape.
Wine grapes, on the other hand, are smaller, have thicker skins, larger seeds and have a lot more sugar in them (which gets fermented into yummy alcohol). The thick skins and large seeds also give wine a lot of the additional, more 'complex' flavours.
Kind of like, how cows used to be leaner, faster, tougher creatures; until humans realised that they tasted great; and decided to make the fattest and juiciest of them breed together over many generations. Table grapes, likewise, have been grown to make them much more appealing for humans to eat raw.
But you still want to know what a wine grape tastes like don't you. Sneak a taste next time you visit a vineyard....they won't notice one missing grape.