You apply by submitting the application on the USAJOBS website. Be sure to include some of your personal interests in your cover letter because they can be the deciding factor in the selection process. My boss picked me instead of the other candidates because we both liked to watch movies, so he knew we would get along well. During the interview there will be the standard questions (Tell me about yourself, tell me about a time when you had to overcome adversity, tell me about a time when you had to do a research project).