Learn Romanian: Studenții sunt în clasă. - The students are in the classroom.

In Romanian, masculine plural words often end in -i. The base word is student, and 'students' is studenți. To say 'the students,' you add a second -i to the end, making it studenții. So the first i makes it plural, and the second i adds 'the'.

I learned that sunt means 'I am.' Why is it used here for 'the students are'?

The verb a fi (to be) is special in Romanian because the 'I' form and the 'they' form are exactly the same. Eu sunt means 'I am', and ei sunt (or ele sunt) means 'they are.' Since studenții is a 'they', we use sunt.

The translation says 'in the classroom,' but clasă doesn't have the 'the' ending (clasa). Why?

In Romanian, when you use a short location word (a preposition) like în (in), pe (on), or sub (under), the noun that follows usually drops its 'the' ending. Even though you mean 'in the classroom', you just write în clasă instead of în clasa.

Does clasă mean the physical room or the lesson?

It means both! Just like in English, clasă can mean the physical room (the classroom) or the educational period (the class). In this sentence, because the students are physically 'in' it, it refers to the classroom.