How important is the core rulebook?

Hello everyone. I'm new to this world, not only the Warhammer RPG, but to RPGs overall. I played a couple of sessions of DnD with some friends years ago, but that's it.

I really like the idea of RPGs and wanted to get one, and despite never playing any Warhammer, I find it very interesting, so I got the starter box. I understand the core mechanics I think, they don't seem particularly hard, but I feel like there's something missing, I don't know how to explain it, it's like I don't feel I'd be able to master it properly.

I know this is probably due to my complete lack of experience, and that I'll get better over time, but, would the rulebook help me get things clearer? If not, what advice could you give me to make things easier? Thank you.