A collection is an object whose primary function is to store a number of like objects. An object called CarCollection may contain any number of Car objects. Collections can traditionally be accessed in the same manner as arrays, which means CarCollection[n] represents a particular Car object. This is true in C#, Java, and more - but not PHP, unfortunately. Since PHP has only recently begun to develop a package of built in objects (the SPL, Standard PHP Library), the ability to support collections in the accepted behavioral sense is very limited.
Their mission is to work with a datatype that PHP does have to simulate this kind of collection handling - arrays. They walk you through the creation of a foundation class, one that simply allows you to get and fetch from the array. Extending that makes it possible to create a customized method for sorting personal data (name).