You can use just about any type of salt but make sure it is a minimum of 99% NaCl, without any additives for rust prevention. Avoid road salts, as it contains alot of impurities.
If you use salt with the ingredient to prevent the salt from clumping, called YPS - Yellow Prussiate of Soda, make sure you brushing to until it dissolves.
The fastest way to dissolve it, with any kind of salt, is to turn your pump on and open the bottom main drain. Add the salt in the deep end over the main drain and brush the salt into the main drain.
However, always consult with the manufacturers instructions in the owners manual. Some systems cannot be powered on when adding salt.
The yellow bags typically have salt pellets, which dissolve more slowly than the crystals. This is not normally a problem as even the pellets will usually dissolve quickly enough. At worst you may need to brush them around a little till they dissolve.