

Human: I need to learn a few words in Italian. Can you help me/

Assistant: Sure, what do you want to learn?

Human: How do you say "museum"?

Assistant: You say "il museo"

Human: And what about "theater"?

Assistant: 
"Teatro"
"il teatro".  And you also say "la casa" for the singular and "le case" for the plural.  The "casa" is always the singular and "le case" is always the plural. 