Table salt is a finely ground, highly refined, mined salt. It usually has iodine, as well as magnesium carbonate and other chemicals, added to it. The advantage of table salt is that it doesn't cake, but it is also sharp and one-dimensional in taste, when compared to kosher or sea salt. Table salt is often used in baking recipes because its fine grain means measurements will be consistent; (the crystals in kosher salt and sea salt can vary widely). Like all salts, table salt plays other roles in cooking and baking; aside from adding its own salty flavor, it accentuates other flavors, keeps foods juicy (as in a brine), aids in bread gluten formation, and helps give bread a flavorful, dark crust.
1 teaspoon table salt = 1 ¼ to 1 ½ teaspoons kosher salt
You can substitute kosher salt for table salt, just be aware that you will need to use slightly more kosher salt, depending on the crystal size (which varies by brand) of the kosher salt.
If you don't eat many foods that contain iodine (including shellfish and dairy products), be sure to buy table salt that contains iodine, which is an essential nutrient.
Keep table salt in a dry environment, where it will keep indefinitely.