Billy Collins's poem "Introduction to Poetry" is heavily metaphorical. Collins uses figurative language, mostly metaphors, to contrast what he thinks students/readers do when trying to analyze a poem with what he as teacher/poet wants the readers to do when analyzing a poem.
In lines 1-3, when Collins wants "them" to hold the poem "up to the light / Like a color slide," he uses a simile to suggest that readers should look very closely at the poem and examine it in depth. When he says he wants them to "press an ear against its hive," Collins uses a metaphor to express his desire for readers to listen closely to all of the activity within the hive. The image of the hive itself suggests a busy, thriving environment, but the reader must approach it from the outside and on its own terms.
The next section of the poem, lines 5-8, includes metaphors that compare a poem to a mouse's maze/labyrinth and to a dark room. In both cases, Collins suggests through the metaphor that the poem is a complex space but that a reader can "find a way out" once he or she can unlock the key to the poem's meaning (the light switch in line 8).
The metaphorical water-skiing in lines 9-11 suggests that Collins wants the reader to see analyzing poetry as a pleasurable experience, one in which the reader acknowledges the poet's influence but is not tied down by it (the reader is free, sliding across the surface).
At this point in the poem, Collins employs a tone shift and while he still uses figurative language -- personification and metaphor -- the comparisons made here take on a much more sinister feeling. The poem is now compared to a person being tortured and interrogated. Readers, Collins says, want to "tie the poem to a chair with rope / and torture a confession out of it" (13-14). Collins depicts readers physically beating the poem ("with a hose") to try to get answers out of it. This is definitely a stark contrast to the previous water-skiing image. Here, the readers have taken all of the pleasure out of reading poetry. The poem suggests that the ineffective "hose" will never even yield what the readers expect it to. The poem does not have one meaning that it is withholding until tortured enough to spill its secret; instead, the poem should be a playful space. Ending the poem with the darker metaphors, however, indicates that Collins may not be very hopeful that his desire that readers enjoy analyzing poetry will be fulfilled.