"Is that our teacher?"
Translation:Это наш учитель?
Этот is used as "this (noun)," where the noun is masculine. Этот стол = this table. Это is used for "this (noun)" where the noun is neuter. Это озеро = this lake. Это is also used as a general "this" or "that" like in this example (What is this/that? This is a (noun)), and you don't you have to change the gender. Это I think has other uses as well, but you get the idea.