Subscribe to mqtt mosquito from PHP

I never used mqtt and I need to subscribe to a mqtt server and save the data from the messages i get, to a MySQL database on a server hosted in hostgator using PHP, javascript or something that runs always on the server (even if i dont load the php or html code on a browser)

i found some libs and wrappers, but don't know how to use them.

http://ift.tt/1k6VVHM

http://ift.tt/1jVJQQ7

How do i install mosquitto-PHP in a hostgator server?

The php with the subscribe code have to be open to be able to listen the publish messages?

Thanks