The subject of an active verb performs the action.
The Minotaur lives inside a labyrinth. [present tense]
The Minotaur lived inside a labyrinth. [past tense]
Theseus kills the Minotaur. [present tense]
Theseus killed the Minotaur. [past tense]
Some active verbs are TRANSITIVE and some are INTRANSITIVE. A transitive verb is one that takes an object, while an intransitive verb does not have an object.
The verb "to kill" is transitive, which means it can take an object:
Theseus killed the Minotaur.
object: the Minotaur
The verb "to live" is intransitive, which means it cannot take an object:
The Minotaur lived inside a labyrinth.
When a verb is passive, it means that the subject of the verb does not perform the action. Instead, the subject is the object of the action.
The Minotaur is killed by Theseus. [present tense]
The Minotaur was killed by Theseus. [past tense]
verb: is killed / was killed
To put an active verb into the passive voice, you use the past participle along with a form of the verb "to be." Often the past participle ends in -ed as in these examples:
The Minotaur was killed by Theseus.
Theseus was helped by Ariadne.
Ariadne was abandoned by Theseus.
Sometimes, though, the participle is irregular and does not end in -ed:
The labyrinth was built by Daedalus.
Theseus was sent from Athens to Crete.
As a general rule in storytelling, you should use active verbs! This post contains some more examples: Examples of Active and Passive Verbs.
Theseus kills the Minotaur.
The Minotaur is killed by Theseus.
Theseus fighting the Minotaurby Étienne-Jules Ramey (1826).
Web Source: Wikipedia.