Final Fantasy XIII/Techniques

You can acquire techniques through the ../Crystarium/, where they look just like ability crystals. The difference is they have no ATB cost, but instead require TP. You can use any techniques the party leader has learned during battle, by selecting the Techniques tab from the battle menu. Also included in the Techniques tab is the Summon technique, which isn't found in the Crystarium, but it available once the character has fought and beaten their Eidolon in the course of the story.

Dispelga
This technique removes all status effects from both allies and enemies. This is a useful technique for when you don't have enough TP to call your Eidolon, which also removes all status effects. If an enemy is immune to Dispel, this technique won't work on them, but it's still good for removing your party's debuffs when you have too many to handle.
 * TP cost: 1

Libra
This will likely be your most used technique, as gathering enemy intel is of paramount importance for winning battles. This technique will scan a single enemy, giving your relevant data on its strengths and weakness, and stagger information. You may not get everything from a single scan, but you'll get enough to inform your Synergists and Saboteurs. Libra also takes a bit of time to finish, so if you don't have everything uncovered when you check the enemy data right after casting it, try waiting a few seconds.
 * TP cost: 1

Quake
A generally useless technique as far as doing damage, as most enemies aren't weak to it and flying enemies are immune. This is a good technique however for getting staggers on every enemy in the battle after a preemptive strike.
 * TP cost: 1

Renew
This is your emergency technique in case something went wrong in battle. If you find yourself needing Renew a lot, it's time to revisit your paradigm deck and work on some new strategies.
 * TP cost: 2

Stopga
Stopga resets the ATB gauges of both allies and enemies. This is really only useful if you know the enemy is about to unleash a powerful attack.
 * TP cost: 1

Summon
Summon allows you to call your Eidolon to do battle. As a side effect, the Eidolon will heal and raise your whole party as well as removing all status effects on both allies and enemies when it leaves. For more information, see the Eidolon page or the Combat page.
 * TP cost: 3