In order for you to create a playlist in a station's media library, you need to be a staff member of that station (or, of course, be the owner).

Creating a playlist 

Navigate to the station's administration panel and click on the 'Media Library' button at the bottom left in order to access the station's media library.

Select the tracks to be added in the playlist and then click on the 'Playlist' menu item on top. 
Create a new playlist by writing a name for your playlist in the 'Add a new playlist' box and clicking on 'Update playlists'.

Your playlist has been successfully created! Click on 'Playlists' and see your newly created playlist with the songs you selected.

Now click on the 'Selected tab' and select 'Clear all selected items' to clear your selection. If you want to reorder the songs in the list, just select a song and use the 'Move up' and 'Move down' buttons on the top of the screen to change their position. Make sure you click 'Save Changes' once you are done.

Now that you re all set you can schedule the playlist in the time slots of your preference. Here is how to schedule a playlist.