Design systems and all

I am a junior UI UX designer and I do graphic design also, for the UI UX for any project I make the components and variables for that project but this is taking time from me and I was thinking creating a design system would help me. As I haven’t made a design system that people talk of which I don’t know, what does a design system include components, variables, style? And when, where and how do we use this in our design project.