Can I buy any HD cable for my flatscreen tv or does it matter?

I have a 32 inch (approximately) insignia flatscreen tv and it sucks to play x of on it. The controls and movements are awful. But the thing is I want an HD cable. Ppl say it should have came with it but I could never find it. And idk if I don't have HD because movies seem like their good quality but I have no idea. But ya the xbox really is bad on it. So if i need another one which one should I get and from which store? Thanks