There are two ways you can add text on the slides: one is by using the Title option and the other is by using the paragraph option:

Title will help you to add a title to the slide. The fonts of the object will be bigger as compared to the paragraph option. Similarly, the paragraph object will help you to add the narrative text to your slide.

Once you drag and drop the relevant object, you will need to double click on the text shown on the object to add your own text. These objects will also allow you editing functions:

Editing options are as shown in the following image: