Salt

Chemically speaking salt as we know it is NaCl (Sodium Chloride) added to which are anti-caking ingredients to stop the salt clumping together.  If you wonder does it make that much difference in terms of baking I would suggest that you make two batches of cake batter one with salted and the other with unsalted butter see for yourself.  Baking with unsalted butter allows you to control the amount of salt.

Sea Salt - Made from evaporated seawater, available as a fine ground or Salt Flakes (Maldon)

Kosher Salt - Large Crystals, the salt itself is not Kosher but it is used to make meat Kosher.

Fleur de Sel - A mild salt made from salt marshes in France it literally means the flower of salt.

Table Salt

Smoked Salt - Salt that has been smoked with a view to adding a smokey flavour to food.

According to the progressivebaker.com 

More than adding flavor, salt begins to affect your baked goods from the moment it's

added to the dough.

Here are some things you should know about what salt does in your baked goods.

• Salt slows down all the chemical reactions that are happening in the dough, including calming fermentation activity to a steadier level.
• Salt also makes the dough a little stronger and tighter.
• Salt impacts the shelf life of baked goods, but its effects depend on weather conditions. Salt is hydroscopic, which means it absorbs water. Consequently, in humid climates, it will trap moisture from the air, making a crisp crust soggy, and therefore shortening shelf life. In dry climates, however, the salt helps hold water in the bread longer, inhibiting staling, and thus extending the bread's shelf life.
• Salt, of course, adds flavor to baked goods. It also potentiates the flavor of other ingredients, including butter and flour.
• Salt comes in several forms, including fine, course, sea salt and Kosher salt. All provide the same effect. In fact, in blind taste tests, people were not able to distinguish a difference in the bread's taste based on the type of salt used.