I truly believe anyone can sing. However, like all academic pursuits, some voice students have more natural talent or aptitude than others.
Initially, it boils down to mimicking sounds. If you have no musical training whatsoever, I recommend you first try matching pitch with sounds around you: sirens, songs on the radio, cartoon voices, anything.
After that, you need some grounding in western musical sounds. The sounds of the western musical scale are very specific, and even some well-trained singers could use more practice in centering their pitches. If you have no musical experience, I highly recommend new singers take maybe a year of piano and join a local choir or chorus. Once that becomes relatively easy, then they could consider private voice lessons. Another route might be to ask a voice teacher if you could take a combination voice and piano lesson -- I'd recommend an hour class for this (30 minutes piano and 30 minutes voice).
Lastly, singing isn't done in a style vacuum, meaning every voice teacher will be trained in a specific style of singing. Unless they were specifically trained by a rock and roll singer, or went to a contemporary music institution, like the Berklee School of Music, you'll get classical training -- the style you hear from choirs, musical theater, and opera.
I hope that helps,
Voice, Piano Teacher