Start from https://www.arduino.cc/en/Tutorial/Foundations and go down to the "Using and installing libraries" part.
It sounds like it would be beneficial to read the whole tutorial from the top. Make sure you try out a couple of the exercises. Make the on-board LED blink. Try to change the blink speed. Try to change the pattern of blinks. Save all those different versions of the sketch with descriptive names so you can come back to them later.