New iOS users may not realize that both the iPad and iPhone feature "undo" and "redo" text options. The undo and redo buttons on the iPad are quite easy to access, while the process of undoing and redoing text on the iPhone is kind of silly.
To quickly delete the last thing you typed on the iPad just tap the 123 key and you will see a large "undo" button next the #+= key. You can now tap the #+= key to access the "redo" button. This works in any text field on the iPad that has access to the built-in stock iOS keyboard.
The iPhone does not feature an "undo" button on its keyboard, instead you can access the "undo" option by shaking your phone. Seriously, just shake your iPhone side-to-side to bring up the "undo" and "redo" pop up box. This feature relies on your device's accelerometer to work, and just like the iPad it works in any text field.
You may find it easier just to use the back button to delete text on the iPhone, but shaking it is a neat parlor trick you can use to impress your friends with your advanced iOS know-how.