How does quantum field theory work?

[EvelynR]

I'm trying to understand quantum field theory but it seems incredibly complex. From what I gather, it combines quantum mechanics with special relativity and treats particles as excitations in fields. But what does that actually mean in practice? How does quantum field theory differ from regular quantum mechanics? What are the key concepts I should focus on to get a basic understanding? And how does it relate to the Standard Model of particle physics?