These eight expressions are often used when something is being renamed or reiterated:
i.e., that is, e.g., for example, to wit, namely, for instance, in other words
The punctuation depends upon where they are in the sentence and/or what follows them. There are six rules; so we will do a few at a time.
THE PARENTHETICAL AND THE APPOSITIVE IN THE MIDDLE OF THE SENTENCE
When any one of these combinations come in the middle of the sentence, put dashes around the combination and a comma after the parenthetical.
...We needed four -- that is, a yellow, red, blue, and green -- to complete the set.
...It was the most heinous crime -- to wit, murder -- that the neighborhood had ever experienced.
Happy punctuating!
Margie