how do I cast on stitches in the middle of a row???
I assume you mean how do you add stitches to a row? That is called increasing. Click on View Videos at the top of this page and select Increasing, there are several methods.
Casting on in the middle of a row can be done in a few different manners. Most popular are reverse loop cast on and knitted/cable cast on, for which you can find videos here on KH.
I also made a video showing how to longtail cast on in the middle of a row.
If you need to add more than one stitch at a time, you would cast on, rather than increase.