mains - Where is the ground/negative for overhead power lines?

I recently learnt that ground can be used to complete circuits using high voltages.

I'd like to know if this is how overhead powerlines work, and if so where exactly do the cables/circuit terminate - at substations or something?

For that matter, the negative (black) mains wire in my house, where does that go?

I had a google around but I wasn't really sure what to look for, hence asking here. If someone can point me in the right direction I'd appreciate it!

Thanks!