How do you do wiith yarn in front and with yarn

I was watching knitty gritty the other day and she show how do it but I caught the tail end I have problem with this if there is pattern that call for it I will not do it ,is there a video on it :grrr: thanks carolyn :hug:

With yarn in front/with yarn in back just means to either have the yarn in front as if to purl or in back as if to knit.