NXT-G is the official programming language for the NXT. Unlike NXC, NBC and NQC, witch are code-based, NXT-G is graphical-based, so it is very easy to learn (however, it takes up a lot of computer RAM, and it makes large program files). Basically, it consists of a line, and blocks the user drags on it and configures, creating a sequence which is executed on the NXT.
A screenshot of a sample program