Essentially, being an introvert basically means that you're more “in your head” than “in your body.” By that, I mean that you spend most of your time thinking and analysing things from a distance, rather than getting your body in front of other people and getting involved.
As an introverted guy, you will most likely be more interested in your own thoughts and feelings and will be less focussed on socialising with others. An extrovert is mostly interested in the physical and social environment and is less focussed on his thoughts and feelings.
You do not have to become an extrovert to attract women or get a girlfriend. All you need to do is become more confident and skilled at interacting with women and you will then have your choice with women.