If you installed it via composer it should be in the vendor/ directory somewhere. There should (hopefully!) be a composer.json somewhere inside it's own folder. Have a look for something like :
"autoload": {
"psr-0": {
"GrabzIt\\": ""
},
That indicates you can use it like :
<?php
use GrabzIt\Client;
class Whatever
{
public function something() {
$client = new Client($options);
}
}
You might need to do some digging though :-/