piano
The word Klavier is used in German to refer to a piano. It is a noun and is used in the same context as the English word piano. For example, one might say 'Ich spiele Klavier' which translates to 'I play the piano'.
I like to play piano.
In this example phrase, the German word 'Klavier' is used to depict a hobby or a favorite activity. The verb 'spielen' means 'to play', 'gerne' means 'gladly' or 'with pleasure', thus the sentence translates to 'I like to play piano.'
The piano in my room is very old.
In this case, 'Klavier' is the subject of the sentence, preceded by the definite article 'Das'. The sentence describes the piano's location ('in meinem Zimmer' meaning 'in my room') and its age ('ist sehr alt' meaning 'is very old').
Can you play the piano?
This is a question asking about someone's ability to play the piano. Literally translated, the sentence means 'Can you play piano?' where 'Kannst du' equates to 'Can you' and 'Klavier spielen' to 'play piano'.