In short, the idea of experience in Blake's "The Tyger" can be thought of in contrast to the innocence of "The Lamb." 

The narrator of "The Lamb" is a child who sees only the purity and innocence of the lamb, and by extension, nature.  The narrator of "The Tyger" knows better.  There is another side to nature, and this narrator is aware of it.

Since the same being makes both, that means there are both innocence and experience--both lamb and tiger--within the creator as well.  By extension, all creatures contain elements of both lamb and tiger.

Also, as is usual in Blake's collections Songs of Innocence and Songs of Experience, to which both of these poems belong, Blake is dealing with different perceptions of the same thing.  In the case of these poems, he presents two different perspectives of nature. 

For specifics, look at the images created in "The Tyger."  The tiger's symmetry is "fearful"; "dread hand" and foot; "deadly terrors."  And notice stanza five:  the stars cast down are an allusion to Satan being cast out of heaven, and the speaker asks if the creator that fought and won the battle for heaven, then looked at what he had created in the tiger, and smiled. 

The creator of the tiger is no innocent.