you know how in all of them campaign mission where a text box says stuff and it fills up the whole screen? well how do u add them? ive look at some scripts like cor1_c but those scripts just make me more confused lol

Edit: it looks like u enter a code like this and then go to your localizer tool and place text at level.MAPID.objectives.campaign.1_popup? correct?

Correct. You just need that last line for a popup Text to be triggered. The part in the first line is just the setup for a objective. The second line is the Yellow Text you see at the right side of the screen when opening the minimap.
Don't be shy trying out your assumptions if you think they're right.

I'm pretty sure it's ShowMessageText(localizationkeyhere), lemme check.

I'm pretty sure TK432 is right on this. From memory that's exactly how you do it...that's how they do it in the stock campaign anyway. Your way might work too, for all i know.

Well, my way is for the chat text, while the pop-up text is for, well, the pop-up text.

Is the chat text only for multiplayer? Or is it one of those texts that scrolls across the top corner, like when you kill someone? Or is it neither?

The yellow message text, basically, or even simpler, yes, the multiplayer chat text "theme".