Mostly in the lines, it gives you games to play related to the ride line. For instance, my family of four had fun in the Soarin' line as we joined a color team and answered Geography trivia. The app also had some Toy Story related games to play in the Slinky Dog line.
But in Galaxy's Edge, the Play app became a whole different thing and let you translate the language, hack door panels, etc. It made you feel like you had a data pad and you were more immersed in the environment. It was fun our first and second tries, but eventually the kids gravitated away from it.