You are on the RS of the fabric when you cast off the middle stitches, then finish this row. You’ve done that.
The next “right side” means the right hand side of a top as you would wear it. This is the side with the yarn still attached. You are only working this half from here on. You will return to the left half later.
K across 1 row. This is the WS row.
So you are back on a RS row.
Dec at beginning of row, work row.
Work WS.
Repeat
I personally don’t like the way this is worded but not everything can be written to my taste.
I hope this helps