A Parenthetical is a direction to the Actor about how to read the Dialogue.
Here are some samples of dialogue with Parentheticals:BOB (sarcastic) Of course I love you.MARTHA (trying not to explode) Can't you be serious for once? (a beat, then) Wait, who are you?
Here are some bad Parentheticals:MIKE (reaching for gun to shoot the alien) Stop!HARRY AND SALLY (they keep arguing as they walk out the door) Am not. Am too. Am not. Am too.
What makes the second examples "bad" is that they're describing Action, not giving information to the actor about reading the line. In other words, proper format asks you to not do this:ZEKE I don't think you should stay (he cocks his shotgun) We don't want you here.
but instead do this:ZEKE I don't think you should stay.He cocks his shotgun.ZEKE (continuing) We don't want you here.
Notice the "continuing" Parenthetical above. You put those in when a character's dialogue is split by Action (or, sometimes a Shot.). Some studios insist on these, some insist you don't use these. So, again, I would use them unless I had a specific reason not to.
If you had other Parenthetical direction to add, you would put it after the "continuing" like this:ZEKE (continuing; calmly) We don't want you here.
Parenthetical margins are 3" from the left and 3.25" from the right. If a Parenthetical takes up more than one line, indent the lines after the first 1 character so that the text on all of the lines start in the same vertical column.
Creating a Parenthetical is easy. If you're in Dialogue, just press <Tab> or the "(" key. Scriptware will change the margins and spacing appropriately and all you do is type.
To return to Dialogue from a Parenthetical, just hit <Enter>.