Current questions and answers regarding the map editor.

I don't understand where to write this? I haven't created any scripts in this editor before, please explain in more detail. I need the text to appear once at the start of the game for the red player.

Is it a single-player game?
You need to write it here. Open MapProperties (you can probably just press the spacebar in the editor), go to the Script tab, click Edit, and edit it in the text field.