In by Edgar Allan Poe the speaker says I marveled this ungainly fowl to hear discourse so What does mean?

The word "discourse" in this context means "to speak in a formal or serious way". The speaker is surprised that the raven, an ungainly (awkward or clumsy) bird, is able to speak in such a formal and serious way. This is also a form of personification as the speaker is attributing a human ability to a non-human animal.