I have a samsung galaxy s5 and I have added music from my laptop to my micro sd card and I can play the songs individually by going to the folder in my files but they do not appear in the pre installed music app
Restart the phone. You can only play what's in the media database wen you use the player app, and the database doesn't get rebuilt when you copy files, only when you start or restart the phone or do something media-related, like record something or take a picture (or run media.Re.Scan to force a rescan, which is how I do it).
(If the music app had to scan everything to find all the music files every time you ran it, you wouldn't be happy - scanning takes time.)