Basically, you take an object:

$obj = new ObjectWithChainableMethods();

Call a method that effectively does a return $this; at the end:

$obj->doSomething();

Since it returns the same object, or rather, a reference to the same object, you can continue calling methods of the same class off the return value, like so:

$obj->doSomething()->doSomethingElse();

That's it, really. Two important things: