Welcome!
They will be asking questions on your drinking/using history and the consequences thereof. Don't sweat the inpatient/outpatient options, go with their recommendations and they can improve your chances of being successful. Inpatient is a very common recommendation for many reasons including the detox process which can be very dangerous. In addition to the detox process many of us simply cannot stay away from our alcohol/drug by ourselves. I have known many people like this who have tried outpatient and not been successful at resisting early on.
Make sure you follow up with a program of recovery. A 30 day rehab is wonderful but you really need a program of recovery to maintain sobriety. Many people like myself used a 12 step program and found it to work.