How can i add or draw text?
That would depend on the context. If you want to print text to the screen for a limited duration, you can simply use the print function, which is also what is used to print to logs.
If you want something more permenant, but local to the player only (such as a HUD) you would need to use UMG.
If you are wanting to print text on a third party object, that is visible in the world, use a Draw Text node.