"You are sitting."
Translation:तुम बैठे हो ।
बैठना is a used as a stative verb in Hindi. So, you normally use the present perfect form 'बैठा/बैठे/बैठी है' to say that someone is seated. This is similar to how in English you say 'I know the answer' instead of 'I am knowing the answer'.
The present continuous form of बैठना, which is used infrequently, is used to indicate that someone is in the process of sitting down.