I have a question regarding about the Security Clearance at a Air Force in US. I have phone interview next Monday and I do not possess a security clearance. Do jobs requiring a clearance require that I have one before starting, or can I get one after the job is offered? What is the process and what are the requirements?

The job for which I am interviewing is in another state and where I live there is a military installation nearby, about 30 miles from my home.

If I get an offer and need to do the security clearance, can I go to the base near my home and apply for the security clearance there?