Dialogue is simply every word we hear on the screen. Everything that comes out of everyone's mouth (whether we see them on the screen or not).
Simply, write what you want your characters to say.BOB But I don't know what to say. It's not like I, well, it's not like this is something I enjoy.
There's not a whole lot of advice to give here beyond the ever-present, "show it, don't tell it." Apocalypse Now could have been a guy's head, on the screen, as he narrated the story, but who would pay to see that?! Same thing in your dialogue: see if there's a way to write so that we get to see something rather than hear someone talk about it (unless you have a good, dramatic reason, to not show us... ooooohhhh, mysterious).
In a similar vein, be careful of monologues. Readers get a bit concerned when they see a page that's 99% Dialogue. After all, for movies and TV shows at least, we want to see something beyond a talking head. If you have a monologue, ask yourself, "Are there ways to break this up with some action (either the speaking character's, the listening character's, or something in the environment)?" Breaking up a monologue makes a page read faster and, remember, we want them to keep turning the pages!
Dialogue margins are 2.5" from the left and 2.5" from the right.
After you've typed your Character Name or Extension, just press <Enter> and Scriptware will put you in the right place to start typing your Dialogue... just type away.
When you're done with the Dialogue, press <Enter> (there are other things you could press, but that's the thing you'll do most often). If you're typing a Parenthetical, pressing <Enter> will bring you back to Dialogue, as well.