Simply clone or download this code and run the PHP inbuilt browser
PHP -S localhost:8080
visit http://localhost:8080/ in your browser.
You can experiment with the SongCollection or AlbumColection class or use them as the basis to create other collection classes.
For example, why not try to create a ConcertsCollection, and add properties and calculations for TicketsSold, TicketsRemaining, AverageTicketsPerConcert etc
REMEMBER the strength of the collection, over the array as that it is made of more than its members. Collections can gave properties and methods outside of the members.