Salt is more than just a condiment, it plays an important role in bringing out flavours in recipes.
There are two main types of salt:
Sea salt: made by evaporation of sea water
Rock salt: extracted from mines
These two kinds are then factory refined to produce the very fine white powder that we know as table salt. Unfortunately, this refining results in the loss of most of the minerals and its characteristic flavour. That's why if you don't particulary need fine salt, it's better to use unrefined coarse grey salt.
If you intend to buy: I advise you to keep at least two kinds of salt: coarse grey sea salt (like "Sel de Guérande"), and a finer salt for the times when coarse salt is unsuitable.
If you want to use it: Don't forget that for an equal weight, white refined salt adds more salty taste than coarse salt, so you should add less of it.
You can make yourself a special salt with a particular flavour, as you make vanilla sugar. It's possible to make salt with herbs, citrus fruits or chili.