Based on https://listamester.hu/docs/pubApiDoc.txt
Add to your system the constants from config.php and include the class.listamester.php
$listamester = new Listamester();
// get our groups -> return groups in an array
$listamester->getGroups();
// check member exists in the group -> return true / false
$listamester->memberExists('[email protected]');
// get member datas -> return array
$listamester->getMember('[email protected]');
// subscribe new member -> return true / false
$listamester->subscribe('John Doe', '[email protected]');
// change default group ID
$listamester->groupID = 12345;