It's an enjoyable TV show about a group of students who are part of a 'glee club', i.e. a more modern version of a school choir, who are attempting each series to win various awards against rival glee clubs from other schools and fighting off the cheerleading coach/evil gym teacher, who resents them and the teacher in charge because they're taking funding away from her and her bratty cheerleaders.
It's also a show that gets unfairly bashed for various reasons by ignorant people who refuse to accept the mere existence of anything that they don't like, even when the show is obviously not aimed at them and nobody is forcing them to watch it or have any knowledge of it.
And for the record, the songs on the show are actually pretty good, purely because the actors are generally good singers (hence them being on the show in the first place), and many of them are already rising stars within the field of musical theatre, a worthy profession in itself. That being said, the originals are usually better, but that doesn't necessarily mean the covers are crap, because they generally aren't. So yeah...