Well for starters, if you try to tell someone what poem you've been reading, you'll always have to repeat yourself. No one ever understands the title of this poem the first time you say it out loud, and hardly anyone can even recognize that it's a person's name. But that's exactly what it is.
Now where does the name Hugh Selwyn Mauberley come from? Well your guess is as good as ours. The one thing we can say is that the name "Selwyn" might be a tribute to the English poet Selwyn Image, who Pound actually pegs as one of the "good guys" of modern literature in line 131 of this poem.
In writing "Hugh Selwyn Mauberley," Pound is doing something really similar to what T.S. Eliot did with "The Love Song of J. Alfred Prufrock." He's creating a fictional character (who's sort of just Pound in disguise) and using his life and the people he meets to illustrate just how terrible the modern world is.