You will make an appointment with the consulate ahead of time, and go in that day for your visa. They will probably tell you that day whether or not you have been approved for your nonimmigrant visa. If you are approved, it will take about a week to process the visa.
If you are put into administrative processing, they want to check on either some type of security clearance and verify that the application is correct. The process can take up to three months.
If you are going back for an immigrant visa and you are going to process it at the consulate, it should also take a short period of time.
Each consulate has their own rules, and it is important to go over those rules with your immigration lawyer to make sure that you are ready for your visa interview.