1. Take a careful look at the design once again. The diagonal lines are orange when you start. But once you turn the corner, they are green. This could confuse you a bit.
2. But this is simply because the diagonal lines are worked initially and left to be worked on the return trip once you turn the corner.
3. To fully understand this, work the pattern once in 2 colours and then once more using a single colour.
If you have any trouble following instructions, leave a comment and I'll help you out.