Orange interview questions

Face à face avec le manager du site et la DRH, connaître les motivations et les envies futures, connaître ma personnalité sur ma facilité d'adaptation et mon intégration dans une équipe

I've passed my first interview, and there are two left. I assume once I pass the two remaining ones HR will call me and make me an offer. Do I have to answer instantaneously? Can I say something like "okay, give me a few days to think about it" and let company A know about it and let them decide if they counteroffer? Can the offer expire? How should approach my current employer to inform them about the new offer?