SIDEBAR FILES LOST

MAC 10.10.5

I HAVE LOST THE FOLDERS THAT I HAD ON MY SIDEBAR, FOLDERS I HAD GIVEN A NAME TO. CALLED APPLE AND INTERNET PROVIDER TO NO AVAIL.YOU KNOW, I OPEN A FOLDER ON THE SIDEBAR, GIVE IT A NAME AND THEN I FILE ALL E-MAILS FROM OR TO THAT PERSON IN EACH FOLDER I HAVE NAMED. CAN ANYONE HELP?