While using Presenter View, you can not read directly off your slide due to the only display being too small. But Google incorporated a solution to this problem, Speaker Notes.
A Speaker Note is written text that can’t be seen by the audience, used to assist speakers while presenting. To create one, you must begin by being in the editing screen for your slide. Then, click on the text below your slide that says, “Click to add speaker notes”. Proceed to type whatever you want your note to say. This must be done for each individual slide.
To use Speaker Notes, have Presenter View up and running then click the “Speaker Notes” tab at the top.
While using the Speaker Notes, it will automatically display the notes you’ve written for your current slide. You can also increase or decrease the size of the text with the addition sign (+) or the subtraction sign (−).
One thing that is important to note about using Speaker Notes is that you cannot edit your notes while presenting. All notes must be written before you present.