LG G2 America Sprint Version not working properly in India

My brother gifted me an old phone which he was using in America. The LG G2. I think it had some sprint contract initially. When I got the phone I was unable to use my IDEA sim on it. So I visited a local mechanic. He said that it will have to be unlocked. I paid the charges and he gave me phone after a few days. It wasn't working well from that day. I thought maybe its hardware is not so good. And then, one day it stopped saving call logs and giving and error like unfortunately google process has been stopped every time I called someone. Then I visited some other mechanic who previously worked in Samsung Service Centre. He said the device is not unlocked properly. And he has to unlock the device again. For that he started to download some LS980ZVE file from the internet. I peeked into his computer. When I saw build version in my mobile it was previously running LS980ZVE. I didn't interrupted. And paid the charges in advance. Today he called me to visit him. He said that he has installed the new software file he downloaded but when I tried it wasn't accepting my SIM. I tried another SIM but the result was same. He scratching his head said that maybe the device has gone to locked state again. He said me to leave the mobile with him as he will give it to me unlocked tomorrow. But now I am keen that if I can do the unlocking at home. I had a friend who is an engineer. He always talked about unlocking, rooting, jail-breaking etc. He always said that it was a easy job. I couldn't get in contact with him. Then I started searching on google and finally saw XDA DEVELOPERS. I thought of finding a solution here. But couldn't understand a thing. I hope if you people can help me about it.
If you could give me a permanent solution to the problem. Also if I could get latest android version working on it.
Even if there is no permanent solution I am keen to know more about this unlocking thing. How it works and what it requires.
Thanks in advance.