Apply through USAJobs. Wait to be referred. Once referred, HR will contact you to setup an interview. Once you have the interview, you will meet the supervisor and other co-workers.
I applied online. I interviewed at US Department of Justice (Sacramento, CA) in Oct 2015
Interview
Department manager and most senior tech had the interview. Asked me a few standard questions, but were mainly concerned about the personality fit and teachability of the prospective employee.