ffc Squall

First, make sure that the field skill that you want to use is equipped like any other skill. Then, go to the Overworld or anywhere else with monsters and press RT. After that, scroll down to the field skill section of the menu that will pop up and select the button that you want to assign the field skill to (either LB or RB). Then select the field skill and exit out of the menu. Finally, press the button you assigned the field skill to to use that field skill.

Warning! Field skills use up MP very quickly, so use them sparingly!