Can someone help explain hyperspace and hyperspace travel in Star Wars to me? I've read the wiki but am still confused. Is it an alternate dimension? If so, how could the Raddus hit the Supremacy?

Hyperspace was always a bit confusing to me, but after The Last Jedi I'm very confused.So what I've gathered from the Wiki is that when you go to lightspeed(?) you enter hyper space where you can travel infinitely quicker and appear somewhere else. There are "hyperspace lanes" where you know it's safe to engage hyperspace and go until you appear somewhere else. I think I understand that part...albeit it's still a bit confusing because I don't know what exactly hyperspace is.But in The Last Jedi, Holdo goes hyperspace/lightspeed and rams the Supremacy. However, when she set the ship to go lightspeed, shouldn't it have gone into hyperspace and thus not in the same realm as the Supremacy? That's the part I'm confused about.Thanks in advanced. Any other hyperspace info would be great! via /r/StarWars https://ift.tt/2KThbTy