Autunm, I think you're really smart to work with a personal trainer. Trying to learn how to lift weights from a book is kind of like trying to learn how to play tennis or the violin from a book -- difficult! It's so much better to have someone teaching and correcting you in person.
The trainer should start off by asking YOU what your goals are. That's the very first question that everything else will flow from. Tell him your goals and then tell him that you need helping developing a program to meet your goals. He should take it from there. His job is to put together a program that will help you achieve your goals.
If you feel like you need help in a special area, don't be shy about pointing it out (like if you like free weights but feel totally intimidated or something like that). You could ask about how you can measure progress, like regular body fat checks and tape measure measurements.
He'll probably ask you how much time you can commit to the gym each week -- 3 days? 4? 5? 6? -- so that he can put together a balanced program of cardio and weights for each time you come to the gym. He might want to talk to you about your nutritional program since your goal is weight loss. He may put you through a basic fitness assessment to evaluate your current strength, flexibility, and cardiovascular fitness. Don't panic, it's not a test! Everyone has to start somewhere.
But don't worry about asking him questions! He knows what to ask you and then he'll be able to give you the right answers.
Good luck tomorrow and let us know how it goes!