Figurative language is an overall term used to describe various types of writing techniques that authors use to make their writing more interesting and more descriptive.
Kinsella's text in Shoeless Joe especially uses the figurative techniques of metaphor and simile. A metaphor is a comparison between two things that don't appear related. Metaphors can be useful when an author wants to convey understandings and impressions beyond what would be understood with a straightforward description. Consider this description of baseball and the action within a game.
Within the baselines anything can happen. Tides can reverse; oceans can open...Colors can change, lives can alter, anything is possible in this gentle, flawless, loving game.
A game of baseball won't actually make tides, oceans, or colors change - but Kinsella vividly expresses the potential that awaits the start of every baseball game.
A simile makes a comparison between two objects directly, usually using the words "like" or "as" to connect the two items. One object is more completely understood by the reader as a result of its comparison with the other. "I feel the night rubbing softly against my face like cherry blossoms" explains the softness and the sweet aroma of the night air at the baseball field.