Adding multiple of mp3 to an intro

CAN SOMEONE PLEASE HELP ME TO FIND A WAY OF ADDING MORE THAN ONE MP3 TO AN INTRO?

I CURRENTLY HAVE ONE BACKGROUND MUSIC PLAYING IN THE INTRO.
I NEED TO ADD 3 MORE MP3 TO THAT INTRO.
AS SOON AS THE FIRST INTRO STOP PLAYING, I WANT THE NEXT ONE START PLAYING AUTOMATICALLY AND SO ON … THEN START AT THE FIRST SONG AGAIN UNTIL THE PERSON CLICK SKIP INTRO TO LEAVE THE PAGE.

I REALLY APPRECIATE IT