How do I know if this girl likes me?

hello girls I'm a 21 year old guy. I'm single and I never really had a girlfriend in the past because I was very shy and I still am. I usually go to a fast food place where I noticed this girl who always brings me the drinks and she is very pretty and friendly. I have a crush on her but I'm afraid to tell her. last time she was delivering me drinks she looked at me and smiled at me and then asked me how I was doing I said great and then I asked her how was she doing and she said great as well. did the smile mean anything? how should I approach her? I'm a very shy person when it comes to girls.