Stupid question - what is a voting rep and why should I change it? And what should I change it to?

I am relatively new to crypto currency. I had a Bitcoin wallet a few years ago but was pretty put off if it when I realized I had to download a multi-gigabyte blockchain before I could even start using it (rural internet was hardly any better than dialup then).

I heard about Nano when a post from this sub hit the front page a few months ago and it piqued my interest. I've never owned any until a few days ago when I finally got Natrium/Shakepay. I was blown away by how fast it sends, and the fact that I don't have to download an ever expanding blockchain file. This is what crypto currency is meant to be.

Anyway, I have done a reasonable amount of googling to try to understand what a voting rep is and why I should change it but haven't been able to find any clear answers. Where do I even go to change it, and are there good reps and bad ones?

I probably have lots more stupid questions so if anyone is aware of an idiots guide to nano I'd be happy check it out. I have read everything I can find on nano.org.

Thanks in advance.