explode function creates an array of data from whichever bit of the data you wish you create it from...

explode("@", "a@b@c@d"); would create an array of 4 parts ("0" being "a", "1" being "b", "2" being "c", "3" being "d")

Counting In PHP always starts at "0", If "@" was the first charater in the explode string "0" would be null

Click Here For Further Explode Help