How are volerci and metterci used?
With time expressions in Italian to express the amount of time it takes to perform an activity: to take (a length of) time. It takes two hours to get there by car. It takes me four hours to get there by bus.
How is the subject of volerci defined as?
The amount of time in question. It can be conjugated in all tenses, but it has only third-person forms, singular (ci vuole, ci vorrà, ci è voluto, and so on) for one hour, and plural (ci vogliono, ci vorranno, ci sono voluti, and so on) for two or more hours. Notice that volerci takes essere in the compound tenses.
Ci vogliono tre ore e mezzo per andare a Milano da qui.
It takes three-and-one-half hours to get to Milan from here.
Ci vogliono tre ore per andare a Napoli in macchine mentre in treno ce ne vorrebbero cinque.
It takes three hours to go to Naples by car, while it would take five by train.
What is the subject of the verb metterci performing?
The action. Thus metterci can be conjugated in all persons and tenses. Metterci takes avere in compound tenses.
Ci hanno messo tre ore per scrivere la relazione.
They took (It took them) three hours to write the paper.
Tu sei veloce! Io ci metterei due ore per pulire questa casa!
You are fast! I would take (It would take me) two hours to clean this house!