I can;t find where to go.Is it in Blackreach?I see it on the map but can;t find it.Sepimus Signus sent me.

Are you in Blackreach? It's in a place that is accessible through Blackreach, but not in Blackreach itself. It's in the Tower of Mzark, which if you came to Blackreach through Alftand will be on the very far end of Blackreach. Blackreach is a huge place and it took me forever to figure out where I had to go, because since you're technically in a dungeon and not outside, the world map won't help you in Blackreach, and the 'local' map won't show the arrow for the Tower of Mzark because it's so far away. At least it didn't for me, anyway.

Is there a faster way into blackreach?

Is it in the Tower of Mzark?

... Um. How hard is it to follow the big arrow on the compass, at the top of the screen?

Sometimes that that Easy.

I found the place.I put the cube in and pushed the button and the main thing spun around but I can't get the other two buttons to work?

Just keep messing with the buttons working your way from Right to Left, as soon as the button to your left lights up, move to that button and repeat until all buttons light.

I wasn't really sure what the solution to the puzzle was, and I still don't now.

Just do what I did and mess around with the buttons until it works