There is the link to the pattern. Okay, so I’m at where it says, “Both mitts: Continue to cast on 2 gusset sts every third row — new st will always be just inside markers. Take new sts into k1, p1 rib. When there are 11 gusset sts,
put them on waste yarn. CO 1 st
Does this mean that before I add stitches I just do the cable stitches and add the gusset stitches where it says to? And is there a certian way I should cast on to add the extra stitches? then what does it mean take the new stitches into k1 p1 rib? Wouldn’t they be at the end of the row?

I’m a new knitter so please help!

Hi and welcome to KH and to knitting.
At the same time that you add stitches for the thumb gusset, start the cable pattern on the back of the mitt.
For the CO1, you can pick up the yarn between stitches from the previous row for a mostly invisible increase.
When you come to the place where you increased stitches in the previous round, work those stitches in k1p1 rib. So for the first round you increase, p1, increase between the markers. On the next round, k1,p1,k1. After the next increase round, p1,k1,p1,k1,p1 and so on until you have 11sts between the markers.
Since you’re working in the round here, you won’t have a end of row, just a continuous round.
Very cute pattern. Post a picture of the finished mitts if you’d like.