Please give an explanation of the following lines from "My Last Duchess."That's my last duchess painted on the wall, Looking as if she were alive....

You have quoted the first few lines of the poem, which
makes it clear that this poem is an example of a dramatic monologue. Note the way in
which the speaker is addressing someone, but although he asks this person questions, he
does not wait for an answer, as is shown by the fifth line. The speaker quickly
continues his narrative and gives no opportunity for the hearer to
respond.

These first few lines then establish the setting.
From the description of the painting as being of "my last Duchess," we can infer that
the speaker is the Duke, and that he has had more than one wife. He also gives testament
to the incredible skill involved in the painting, that makes it look as if the dead
Duchess is actually alive. We are told that a monk painted her and that very few people
actually get to see this painting because a curtain covers it. The portrait of the
Duchess bears an "earnest glance." This beginning therefore raises more questions than
answers. Why is the Duke showing this portrait to his hearer, and who is his hearer?
Answering these questions will help you to unlock the meaning of this rather disturbing
poem.