New Knitter Needing Help

I am a new knitter and I have a quewstion that probably seems silly. I am making a felted purse - large size. I am getting close to the end of the two balls of yarn that I started with. What do I do when I run out of yarn? Do I need to cast on again and then go back to knitting? I think there would be a row that is different if I did that. Thank you for helping out someone who is new to the game of knitting.
:)Mj

You don’t cast on, but just start using the new yarn. You can find a few methods for how to to do that on the Tips page under Joining Yarn.