Salt is so necessary to human and animal life that it has been used as money in certain parts of the world. Most of us encounter table salt in the salt shaker and use it to flavor our food. The shakers are probably filled with iodized salt, which adds trace amounts of iodine as a public health measure.

Sea Salt - notice the lacy appearance
As cooks in a modern society, we walk a fine line with salt. Overconsumption of salt can lead to high blood pressure. Underconsumption can cause muscle cramps, dizziness and possibly electrolyte issues. The public has developed a taste for salt via snack foods that probably leads to overconsumption. Salty & greasy sells snacks such as potato chips & corn chips. Resist the urge to salt to taste - better to slightly under use salt in cooking and let the diner supply more on the table as they desire. I've found that many recipes include salt with little justification, or over specify the amounts.
Salt is commonly produced by evaporation of sea water. Many coastal areas have brine ponds which are filled with sea water and use the sun to evaporate the water over a period of time. Here in the San Francisco bay, the wind blows over the ponds and occasionally creates sea foam. From the air, brine ponds of differing salinity have differing colors due to the brine shrimp and other organisms that thrive at certain concentrations of salt in the water. Most sea salt is recrystallized (refined) to remove high levels of magnesium & calcium compounds
Salt is also mined. High concentrations of salt found in the mountains of central Austria have been mined for millinea near the river Salzach and Salzburg. Black salt is mined in India and contains sulfer.
Individuality - the various methods of production result in differing textures, colors, trace ingredients and tastes. Differing forms of salt are produced as a result of locally occurring trace elements. Pink salt contains iron oxide. It is possible to taste the differences in the origin of handmade sea salt.
Kosher salt is a coarse grained salt used for koshering meat (extracts the blood). Some cooks like to use it as it has few impurities and has not been iodized. It is not suitable for baking as it does not dissolve readily and grains may remain. The weight of kosher salt is the same as regular salt, but the volume will differ.
Salt has been used for meat preservation for centuries. Meat cured this way is usually soaked in water to reduce the salty taste before further preparation.
Rock salt is a very coarse grained salt used in water treatment to produce "soft" water for washing, in winter to clear ice from sidewalks and in the manufacture of homemade ice cream.