Hi Pamela,
1. Yup, first you apply for the job, sort out the details and start working on a model.
2. You can contact the customer directly via "Apply for this job" - the customer is responsible for his job applications and will see all information and your comments from there.
3. This normally defines the model formats that the customer would like to get. This also go well with the previous point - by contacting the customer you will be able to sort out the details.
Hope that helps!
Cheers,
Eddie, CGTrader