Techniques are special commands that can make your battles easier, but they can only be used if you have at least 1 Technical Point (TP) available. TP is recovered by a certain amount at the end of each battle.
Additional techniques will become available over time. More powerful techniques consume more TP when used, and unlike HP, TP are not restored automatically after battle. Aim to achieve high battle ratings in order to replenish TP.
Knowing when to use Techniques is a key strategy during difficult battles. Be very mindful of when and where you use them. As a rule, save them for tough battles only or when you wish to fill out the Libra screen.