Knitting chart help.

[Knitting292009]

Hello I have a pattern chart for mittens I am making. I'm a little confused because it says to take 13 stitches and hold them for the thumb but I don't know when I am supposed to do this. Do I do the 52nd row and then take the 13 stitches after I knit them and hold them off?? ALso when I make the left mitten it says to do it as a "MIRROR IMAGE" wil