The most basic object to display text is a FlxText. You can easily set properties such as text, color, alignment and more. It is an extension of FlxSprite, which means, you can do a lot of the same things with it.

// create a new FlxText
text = new FlxText();
text.text = "Hello, World!"; // set text's text to say "Hello, World!"
text.color = FlxColor.CYAN; // set the color to cyan
text.size = 32; // set the text's size to 32px
text.alignment = FlxTextAlign.CENTER; // center the text
text.setBorderStyle(FlxTextBorderStyle.SHADOW, FlxColor.BLUE, 4); // give the text a 4-pixel deep, blue shadow

Demonstration

package;

import flixel.FlxG;
import flixel.FlxState;
import flixel.text.FlxText;
import flixel.util.FlxColor;

class PlayState extends FlxState
{
	override function create()
	{
		super.create();
		
		var text = new FlxText();
		text.text = "Hello, World!";
		text.color = FlxColor.CYAN;
		text.size = 32;
		text.setBorderStyle(FlxTextBorderStyle.SHADOW, FlxColor.BLUE, 4);
		text.screenCenter();
		add(text);
	}
}