When singers talk about using voice, they--above all--are referring to the timbre of a voice: that quality of a person's voice that makes it instantaneously recognizable. Think of Frank Sinatra.... Think of Orson Welles, especially in his later years, marketing wine. Think of George W. Bush's drawl.
How do you develop a voice? When I studied voice, my teacher told me to sing softly and quietly, so that my natural voice would come out clearly, free of any impulses to imitate the other voices that I heard. I was to focus on developing my voice, not making it Joan Baez's or anyone else's....
Writing teachers often encourage their students to keep journals, composed of writing that they do regularly for themselves. In a sense, keeping a journal is like singing quietly. As a singers progress and their unique voices become stronger, they begin to sing with bolder, louder voices. For writers, the process is often the same. Through journal writing and taking other opportunities to write, a writer's voice can evolve from a more generic sound to one that is much more unique to the particular writer.
A few blogs ago, I wrote about having iPad lust. I gave into my passions last week. I'm using Dragon Dictation now to write this blog entry about voice by actually using my voice to dictate. When you write, can you hear your own voice speaking the words in your head? Listen to yourself, and ask yourself what you sound like.
The first step in developing your own voice is to recognize that you have one and then go looking for it.