Consonants are divided into many categories by phoneticians, but we need
not concern ourselves with most of them.  Picking the correct consonant is
very easy if you pay attention to just two categories: voiced and
unvoiced.  A voiced consonant is made with the vocal cords vibrating, and
an unvoiced one is made when the vocal cords are silent. Sometimes English
uses the same letter combinations to represent both. Compare the th in
thin with the th in then. Notice that the first is made with air rushing
between the tongue and upper teeth.  In the second, the vocal cords are
vibrating also.  The voiced th phoneme is DH and the unvoiced one is TH.
Therefore, thin is phonetically spelled as THIHN while the word then is
spelled DHEHN.

A sound that is particularly subject to mistakes is voiced and unvoiced S,
phonemes Z and S, respectively.   Clearly the word bats ends with an S and
the word has ends with a Z. But, how do you spell close?  If you say "What
time do you close?", you spell it with a Z, and if you are saying "I love
to be close to you." you use an S.

Another sound that causes some confusion is the r sound.  There are two
different r-like phonemes in the Narrator alphabet:  R under the
consonants and ER under the vowels.  Use ER if the r sound is the vowel
sound in the syllable like in bird, absurd, and flirt.  Use the R if the r
sound precedes or follows another vowel sound in that syllable as in car,
write, and craft.