Joining, attaching, or sewing collar:what's what

I am trying to attach a collar to a V neck cardigan. The sweater is stockinetter, and the collar is garter. Any/all suggestions will be welcome. I do not have a clue as to which stitch to use.

Thank you,

Are you saying that you have already knit the collar separately and are wondering how to attach it? Or are you wondering if you should make it separately and sew it on somehow or knit it right on? Are you following a pattern? If so what does it say to do?

if they are already knitted separatly and bound off then it would be best to sew (usng a matress stitch) or do a crochet join i think.
If they are not already bound off how about a three needle bind off?

if the body is knitted but you have not yet done the colar then picking up stitches around the endge and knitting directly onto it would be your best bet.

Woops! Sorry for the confusion. The sweater is completed in stockinette and collar is completed in garter. Collar had decreases on both sides down the front. I did the decreases two stitches in from the edge of collar–so, there is a nice place to work with–just
can’t figure out what will make the nicest join/seam.

Here are pics of similar situation to yours. Note the rev st st and garter don’t have the same number of rows as in the pics.

Just make sure your seam is on the inside/WS. (Altho on some collars the seam is worked on the WS to the shoulders and then it’s on the RS UNDER the collar at the back of the neck…from about shoulder seam to shoulder seam… so there’s a completely smooth area against the body.)