Here is some information about the interview process that I cut and pasted from another site, then modified and updated. United is not hiring for ORD right now, but I think what you are saying is that your interview is in Chicago. The first interview will be with a company called Spherion. I don''t know exactly how it goes, but here is what was posted on the other site:
They ask you to give your name, where you are from, and why you think you would be a good flight attendant. They are looking for good appearance. (For women, a nice dress or a suit is appropriate. For men, a suit is required. They are very strict about this. Don't bother showing up unless you are in full business dress. United is a very conservative company, so sticking to the blue, black, grey family of colors is my advice. Your interview day is not the time to radically experiment with your wardrobe, hair color, or make-up. Ladies, make sure you are wearing tasteful make-up and pantyhose.)
They are also looking to judge how well-spoken you are and what kind of personality you have. Relax, take a deep breath, and smile. They want people who look approachable and friendly. Don't ever trash your previous employer, but talk positively about people you've met or worked with, how much you enjoy serving customers, love to travel, can stay up at all hours and switch time zones... Attitude is everything. At this point you are just trying to get invited for a second interview.
If you are successful at this first interview, within a week or two you will receive a letter inviting you to a group interview in Chicago at Headquarters. They will send you instructions for how to get checked in at the airport. You will fly to Chicago and return the same day. There will also be instructions on how to proceed to the interview site by taking an employee bus. You start the interview session in a group of 10 people or so. They give the group a task to complete in 15 minutes. They are looking to see how well you can interact in a group, whether or not you participate, and what kind of a crewmember you would be. [Keep in mind, as a flight attendant on a widebody aircraft, you will have to be working as a team with 10-15 other people and it can be a long flight to Sydney if you're arguing with everyone on the crew. ] You don't have to be the one talking the most, but you should be participating and offering ideas and constructive criticism when needed. After this is completed, they will call each person in for a one on one interview. This usually consists of about 20-30 minutes of basic interview questions with a few scenario driven questions thrown in. (Ie. You are at the end of a meal service and you have run out of meal choice. You only have beef left and someone tells you they are a vegetarian. What do you do?) After your interview is complete, you are sent home.
If you are successful after this, you will eventually be sent to the closest Medical facility for a physical. They will do a standard work physical and drug and alcohol screening.
If you speak a second languge, you will most likely be given preference in hiring. (Asian languages are more coveted at United due to our route structure and they are hiring Arabic speakers now, but they will still give you preference if you speak any other language - Polish, Italian, whatever you speak.)
Hiring age for United is 21 and 2 years of customer service experience is required. The pay is about $20K the first year ($23 or 24 including per diem) but if you are local in one of the areas they are hiring for (currently BOS and LAX) and can make it through the first few years it does get better. The job is no longer glamorous but it is interesting and different every day. One tip: don't even think about commuting. They are looking for locals or people who can relocate to a domicile city.
United also likes to hire older, second career applicants, so if you feel that you are too old to be applying, you're not! If you have some good life experience, that usually enhances your ability to be a good flight attendant.
They are looking for things like: flexibility and adaptability, passion for customer service, dependability (don't be late!), professional appearance, teamwork, high standards, honesty, great work ethic and cultural sensitivity.
I hope that helps, and good luck! United has been through a difficult time but the training is great (you will get a check for $1500 at the end if you pass everything, go on to an Operating Experience flight and accept the job offer) and the people are very nice.