Your app comes with an intro page, you can find it under Custom Pages => Intro.
This introduction can show anything you want, there are 3 slides and a button as an example. This intro will only show the first time an app user opens the app, it saves an item in browser storage to keep track of this.
You can hide this item in the menu if you don't want it to show, by adding a class of "hide." You must also leave the navigation label as "Intro" for it to function properly.
Here is the HTML for the intro page:
To change icons, you can look at the Ionicons names here, or you can delete the icon and use an image instead.