.COM is the generic top-level domain (gTLD) short for commercial which intended for commercial entities.
.NET is the generic top-level domain (gTLD) short for internet which intended for network provider.
.ORG is the generic top-level domain (gTLD) short for organization which intended for non-profit firms and any other organizations that did not fit under the .com/.net suffix.

2) Does OnlineNIC provide Internationalized Domain name (IDN) for .com/.net/.org?

Yes, OnlineNIC does provide IDN.com/.net/.org domain name. For. org,  10 languages , Danish, German, Hungarian, Icelandic, Korean (Hangul), Latvian, Lithuanian, Polish, Swedish and Spanish are supported.