This is the 759th most frequent Vietnamese word.
ở
"Ở" means "at," "in," or "to live/stay" depending on context.
In this sentence, 'ở' is used to indicate the location where the subject ('I') is situated.
Tôi ở nhà.
I am at home.
Here, 'ở' specifies the location ('school') where the activity ('study') takes place.
Chúng tôi học ở trường.
We study at school.
In this example, 'ở' is used to denote the geographical location ('Vietnam') where the subject ('She') resides.