The infinitive in latin ending, depending on conjugation, -are, -ére, ere, ire, corresponds with the english infinitive "to..." in many ways. It does not involve a person as "sum" might do (I). As in English you may use it as a noun: "Videre puerum puellulis erat gratissimum" - "To see (or Seeing) the boy was very pleasing to the little girls", the infinitive being classed as a neuter noun here, agreeing with gratissimum. Or you may use it thus "Episcopum aram estruere Papae placuit" - "For the Bishop to put up the altar pleased the Pope", here the "Episcopum" is accusative.
Or like English often you can use it with verbs like "posse" (which is irregular) - "to be able" or "cessare" to stop [doing] or "debere" - "must".
"Galli impetum in Romanos facere cessaverunt" - "the Gauls stopped making an attack on the Romans".
Those are some of the commoner uses, hope that helps.