Help with a scarf pattern

Ok. So I’m working on this really pretty scarf for my mom, and I understand all of the abbreviations and stuff, but I find I just can’t figure it out.

Heres the part of the pattern I’m having trouble with:
(after co 21 sts)
-P1, *(yo, p2tog); repeat from * across row
-Repeat step for pattern and work in pattern until desired length is reached or almost out of yarn.

I think what I don’t understand is the yarn over. Should the yarn be in the front or in the back? :??

Thanks in advance for the help, and sorry if this is a dumb question, lol.

For a yo between purls, you need to start with the yarn in front, bring it up over the needle and then back to the front again.