Have you tried one of the tutorials? http://www.scirra.com/tutorials
Making an event to add text when pushing a button is very simple. I'm sure you'll get it after a tutorial. Also, Newline is in fact an expression you can use when dealing with strings. Did you try it? It's also listed in the system object expressions, which you can browse by double-clicking the system object icon at the bottom when entering an expression. You'd use it like this: "Text on first line" & Newline & "Text on second line"