Japanese has many verb pairs where one verb describes an action done to something (transitive) and the other describes something happening by itself (intransitive). For example, 窓を開ける means 'open the window' (someone does it), while 窓が開く means 'the window opens' (by itself or naturally). Transitive verbs use the particle を for the object, intransitive verbs use が for the subject that does the action or changes state. Choosing the wrong verb changes the meaning and grammar. You must memorize which verbs are pairs, and often the ending gives a hint: 開ける/開く, 閉める/閉まる, つける/つく, 消す/消える. Transitive verbs usually end in -eru or -す, intransitive often in -aru or -u, but there are exceptions. When you want to say you did something, use the transitive; when describing what happened, use the intransitive.