Those who work in big companies are also ordinary mortals like you and me. Therefore, there is no need to get nervous as such.
A job candidate is selected based on qualification, skills, industry in which he/she has worked etc. You may apply for the post of HR Executive. However, make sure not to take a job where you will be all alone. Take a job where some senior is there to guide you.
Go and appear for the interview with complete confidence. Numerous job candidates are selected because of their potential and not necessarily on their experience. Possibly your candidature may be turned down because of lack of experience but then somewhere some luck will click. Have a faith on yourself and move forward!
All the best!
3rd July 2015 From India, Bangalore