New knitter

i am a new knitter and found a pattern for a fabric purse. I was doing o.k. until I had to cast on new stitches in the middle of a row. How do I go about doing this?

You use the backward loop cast on (video on this site). You just cast on to the right needle with your working yarn.

thanks for your help I use this sight alot because of there great videos

You can use any cast-on beside long-tail. Backward loop, knit on, or cable, etc. Purl on might be most appropriate, depending on your pattern/row.