It's pretty straightforward, actually. For the bind off part, just do what they say. Knit the 45, bind off 30, and since your yarn will be right there after the bind off, you knit the next 45.
On the way back, knit 45, and then use any one of the one strand cast ons for 30 stitches and then knit the final 45.
You can use backward loop cast on
or cable cast on