You must first fill out a job application. Once that has been done and submitted, wait a couple days and ring them up asking if they have any questions about my application. This shows great interest on your part about wanting the job. The interview will occur when they call you in to gain more information or meet you personally and have a chance to talk with you. Always dress up for these occassions - suit and tie - even if the job is for sweeping up stables.
ob interviews are always stressful - even for job seekers who have gone on countless interviews. The best way to reduce the stress is to be prepared. Take the time to review the "standard" interview questions you will most likely be asked. Also review sample answers to these typical interview questions.
Then take the time to research the company. That way you'll be ready with knowledgeable answers for the job interview questions that specifically relate to the company you are interviewing with.