Hi. I'm not sure whether I can explain well or not, but i'll try.
Many japanese words come in intransitive and transitive verb pairs. But some words can be both intransitive and transitive. In japanese grammer intransitive verb is the word that never takes the "を" particle, while transitive verb needs "を".
For example,
あく intransitive verb
あける transitive verb
ひらく transitive and intransitive verb
examples:
ドアがあく。 The door opens.
ドアをあける。 open the door
扉(とびら)がひらく。The door opens. 心(こころ)をひらく。open the heart
I hope my advice will be helpful for you.