Hi Lisette,
Welcome to the board and to knitting addiction!
To do the next row, your right needle becomes your left needle. Then you have an empty needle (which used to be your left needle), and this needle is now your right needle which you use to knit off the left needle.
Basically, everytime you empty one needle, your full needle becomes your left needle, and your empty needle becomes your right needle.
I hope that makes sense!