Reading fluency is simply the ability to read a book or text clearly. You correct your pronunciation mistakes until you make no errors.
The more you practice fluency, the more confidence you will have because it gives you a safe environment to practise in, increase your reading speed, and to process words faster.
If you are nervous about speaking in front of others, start reading aloud by yourself at home. As you feel more confident, ask a teacher or a native English speaker to give you feedback on more advanced vocabulary.