Tales of Symphonia uses skills known as artes to inflict heavy damage on enemies. these skills are much more effective than normal attacks as such there's a limit to how much you can do them dictated by the TP numerical gauge at the bottom of the screen. Different artes take more or less TP to execute and once the TP gauge is below that limit the arte cannot be used anymore until refilled with restorative items known as gels.
S and T Branches
Symphonia uses a dividing branch in respect to how character learns skills. Characters learn skills by leveling up though what they learn depends on if they fight as a striker or more technical. Most characters start in one end of the spectrum and it takes a lot of hard work to get them to the other side. Genis for example is on the technical side and must do a lot of physical strikes which he isn't good at before his can be considered apart of the S branch. Though if done right a different variety of moves can be learned. This can make subsequent playthroughs a necessity for some.
All characters can use Exspheres these allow characters additional skills called Ex Skills. Which enhances many things from character health and speed to resistence and tp.