To send data from you Arduino to an ESP8266 your first need to send the data over Serial or I2C from the Arduino to the ESP, so i suggest you start there as get that working. Once you have the ESP receiving the data you can then use one of the many examples with a esp library such as webClientRepeating and change the URL to a link of a subdirectory in your website that contains a PHP file to handle the data, of course your need to make that PHP script to GET the data or use POST, GET is faster. if your new to html and PHP then i suggest a website called w3schools www.w3schools.com html and they cover everything for website coding so just use the search and cover PHP get and make it a .PHP page with html code inside else your have to use JS Curl or JS Ajax which i recommend. oh and only servers can run PHP so you wont be able to test if with your browser like HTML.