Just type the title of your hub. The system will give it the address. If the system tells you that the unique web address is already taken, it just means that someone else has published a hub with that title. Change your title a bit. For instance, if 'Going Back to College' was taken (I don't know if it is or not), then you might change it to 'Going Back to College as an Adult.'
Just tweak your title until the system accepts it, but be sure to keep your key phrase or keyword(s) in the title.