Hello!
I am also new to ANDROID. I tried using the app called RINGDROID which edits a ringtone or message tone and saves it to a format compatible with our phone (I'm also a SGA+ user). However, I noticed that it only plays 14 seconds of the tone. And it's kinda frustrating.
However, I found a solution. I uninstalled RINGDROID completely and use this file transfer/management app which basically acts like KIES. But is way faster and better. It's an app called AIRDROID.
What it does is you run the app, and then it tells you to enter the IP address on your PC browser so you can browse your cellphone files and do other tasks.
There is an option there to add ringtones/notifications. All you need to do is to upload the tone to your cellphone via wifi, no need to edit the tones as it will simply transfer the tones to your cellphone, no cuts, no edits and no encodes. Try it. Airdroid is available at Google Play.