At the end of the interview theyll say "do you have any questions for us?"

Ask about the company culture, ask what your duties would be, ask about the team you'd work with, ask about whats coming up in the short/long term, ask if theres anything they're looking for in a candidate not already posted

Be confident, if they're interviewing you you crossed the biggest hurdle already

Be prepared, think about possible best possible responses to questions they may ask

Know about the company you're applying for, they'll probably ask about that

And ASK QUESTIONS, this is a BIG one