@Aspiring: The code tags mentioned are only for this forum to make shared script segments display properly in the reply box. If you don't enclose the script in between the [ code] ... [ /code] tags, everything gets left justified.
As to your original question, the format has developed over the years from different practices. However, the major studios have adopted over time a common format that uses 12 pt Courier with precise spacing. When you follow this formatting, it was discovered that one page is roughly one screen minute. This makes for a useful planning tool. Another benefit is that using "the eighths", a producer can estimate the amount of time a scene requires to shoot.
Your original post used centering. That IS NOT proper formatting. There are actually indents used. You don't need a fancy program to write a script as long as you respect the proper margins.
@Inarius: You are partly right but mostly wrong about including actions in dialogues. You will occasionally see an action included in a dialogue but it is STRONGLY discouraged. It IS NOT used to save space but to indicate an action that co-occurs with a dialogue. Unfortunately, most new writers OVERUSE this. Both Ray and Madhatter used the parentheticals correctly.
Code:
INT. DINER - NIGHT
RACHEL sits across from TOM in the booth. She stare agape as
he trowels the syrup drenched pancakes into his mouth.
A beat. He glances up, pauses and attempts to speak
TOM
(mouth full of food)
Wha..? I'm stah-vin'.
Her head shakes back and forth as he washes it down with coffee.
She spears her sausage link and cuts it before moving it to her
mouth in astonished silence.
TOM
After being stuck in that jury room for
(fork jabs into the pancakes)
twelve effing hours with Howard, I
needed this!
In the example above, the action occurs DURING the dialog. However, that doesn't mean it's generally accepted. In one sense, the dialogue and the action are both "scene shots". Used in this way it passes information to the actor. Some actors dislike it. Some directors dislike it. You're 'directing' from inside the script rather than telling a story.
It could equally be written:
Code:
TOM
After being stuck in that jury room for -
his fork jabs into the pancakes
TOM
- twelve effing hours with Howard, I
needed this!
Some writing gurus will tell you 'never'. It's often because newbies go crazy and substitute it for action lines. Scripts littered with parentheses will often get rejected. It's not about saving space but having a clear, readable script. Actions should occur outside of dialogue. They're shot setups. On the rare occasion it may be needed, be concise. It should add to the immediate context of the dialogue and not be standalone. The situations when you would include an action in a dialogue, though, are extremely few.