Consider a text object "MyText" ... is default text property can only contain standard text such as "Hello!" to display :
Now in your "Project" events layout you can do :
On Start of layout | MyText : set Text to "Hello!" & newline & "world"
to display now :
You can do this to have the same result because "Hello!" is the default text :
On Start of layout | MyText : Append newline & "world"
Don't forget that for display several lines in a text object, this object must have a big height too, and the size change is not automatic !