Json is necessary to complex data management from HTTP and javascript.
However if you want to use Json helper , you need php 5.2.0 or later version.
Encode
Below is encoding sample.
$this->loadHelper('json');
$value=$this->Json->encode(array(a=>1,b=>2));
Decode
Below is decoding sample.
$this->loadHelper('json');
$this->Json->decode($value);