• When you arrive at the airport, you should look for the check in desks, and find one with the name of the airline you are flying on. You will check in and they will weigh your "checked" luggage, i.e. the luggage that you are not carrying on the plane with you. Hold on to your stroller. Then, they will give you a boarding pass. You should look at your boarding pass and find out the gate number: this is where the plane departs from. You will also want to know when the plane departs: you should be at the gate 20 minutes before that time, so you can board the plane.
You then have to go through the security checkpoint. Make sure you are going through the security checkpoint that corresponds with the "pier" you are flying from. Your gate number should consist of a letter and a number: the letter will tell you which pier you are going from. Follow signs toward security and you will get there. You are allowed to carry any amount of formula, but all other liquids and gels and such have to be in their original 3 ounce containers, inside a quart size ziploc bag. They will require some form of identification when you get there: a drivers license is fine. You will have to put your carry on bag through an X-ray machine, and you have to walk through a detector. They may ask about the formula, but you are allowed to have it with you. After that, you should find your gate. Follow signs to your gate number, and sit down in front of your gate. There will be a desk there: you should ask if you can check your stroller. They will put it in the plane and it will be available when you get out of the plane in detroit. When they begin boarding, board the plane.
Towards the end of that flight, you should ask a flight attendant about changing planes. Tell them this is the first time you are flying, and they will explain to you how to get to your next flight. It should not involve the entire lengthy process i described already.
Other than that, when you arrive at Flint, you should follow signs to the baggage claim, take your luggage (make sure it's yours and not someone elses!) and exit the airport.
Have a good trip!