Many textbooks have been written to teach how to speak foreign languages but textbooks can only take you so far, even with the various media of videos and audio files.
The best way is to just face it head on in its natural environment. Go out there, and don't be shy. If you are a beginner, you are bound to make mistakes. More likely, the natives will appreciate your effort to speak their language than pointing out your mistakes and laughing at it.
Children absorb languages very quickly because they are unafraid to make mistakes and are not conscientious about their grammar or pronunciation. Very young children make errors with their own first language. Although adults may laugh at the cuteness, they shrug it off and learn from their mistakes. Adults need to do the same.
Just as a note, if you have taken Japanese in the past, you will have an easier time with Korean. In this book, we will try to show some basics so that you can go into the native environment.
If you wish to test your proficiency in Korean, you can participate in TOPIK (Test of Proficiency in Korean).