In addition to the period or question mark that is required at the end of
a sentence, Narrator also recognizes dashes, commas, and parentheses.

The comma goes where you would normally put a comma in an English
sentence.  It causes narrator to pause with a slightly rising pitch,
indicating that there is more to come.  The use of additional commas, that
is, more than would be required for written English - is often helpful.
They serve to set clauses off from one another.  There is a tendency for a
listener to lose track of the meaning of a sentence if the words run
together.  Read your sentence aloud while pretending to be a newscaster.
The locations for additional commas should leap out at you.

The dash serves almost the same purpose as the comma, except that the dash
does not cause the pitch to rise so severely.  A rule of thumb is: Use
dashes to divide phrases and commas to divide clauses.

Parentheses provide additional information to narrator's intonation
function.  They should be put around noun phrases of two or more content
words.  This means that the noun phrase, a giant yacht should be
surrounded with parentheses because it contains two content words, giant
and yacht.  The phrase my friend should not have parentheses around it
because it contains only one content word.  Noun phrases can get fairly
large, like the best time I've ever had or a big basket of fruit and nuts.
The parentheses are most effective around these large phrases; the smaller
ones can sometimes go without.  The effect of parentheses is subtle, and
in some sentences you might not notice their presence.  In sentences of
great length, however, they help provide for a very natural contour.