My Playlist is a feature found in the Your Playlists section of Your Library tab. To add more songs to My Playlist, simply tap the add to playlist button on the player and choose My Playlist.
As a Free iHeartRadio user, you have the ability to add as many songs as you want to My Playlist, as well as listen to these songs on shuffle.
As an iHeartRadio Plus user, you can have up to 40 songs at a time in your My Playlist. You need to be an All Access user to edit, order, and delete songs from the playlist.
With iHeartRadio All Access there is no limit to the number of songs you can add to your playlists or the amount of playlists you can create.