Summarize this article:

naturally. Sing a note that's comfortable and within your range. Find the note that's in the middle of your register or the note that's closest to your speaking voice or chest voice. This will be a starting point before you go into your subharmonic or lower range.  If you're unsure of your vocal range, read Find Your Vocal Range. Tenor range is in between C3 to B4. Baritone range is usually between G2 and a G4. Bass range is typically between D2 and an E4. Soprano range is typically between C4 and C6 Mezzo-soprano range is typically between A3 and A5 Alto range is typically between F3 to F5 Slide the note slightly a half-note up and then bring your singing voice all the way down to the lowest note you can comfortably sing. Sustain the lowest note you can without your voice cracking or popping. Bring your voice the fifth note from what you were singing. Play a piano note in tandem with your voice so that you can correctly raise the note a fifth. This is the note you'll be in when singing in your subharmonic range. This should also be one octave below your chest voice. If your chest voice is an A2 note, your subharmonic tone should be in A1.

Summary:
Sing any note Slide the tone up and then down to the lowest note you can sing. Sing the note a fifth up from your lowest register.