Is the video lectures starting in between?

in this lecture bhaiya started saying in the last lecture we have studied plot… something like this but in the previous video he taught about sklearn datasets… i am really very confused

when i tried yb[:,1] instead of xb[:,1] it is showing error too many indics for an array … what does this mean??why we can not plot the graph between xb and yb ?? it is showing error they must be of same size?