A metaphor is when something is symbolic of something else. The whole poem is a metaphor: the free bird represents white people, and the caged bird represents repressed African Americans.
Personification is when human qualities and actions are given to non-humans. An example of this is the line, "and the trade winds soft through the sighing trees." It's as if the trees are sighing in sorrow.
Repetition is when the poet uses the same word or group of words many times. One example of this is, "And his tune is heard on a distant the distant hill, for the caged bird sings of freedom."