When you start to pick up sts, hold the yarn end, say about 6 inches worth, in place with your fingers. Once you've picked up a few sts, you can drop the end. It's not going anywhere and if the first few picked up sts seem loose you can give a slight tug on that end to snug them up. The yarn end will get woven in when you've finished the collar.
You're going to pick up sts down the left neck edge, then knit the single stitch off the holder (it's one of the center stitches of the V). Place a marker and then knit the other stitch from the holder. The marker will be slipped from the left needle to the right everytime you come to it. It'll mark the center for decreases. (You can use the holder like a left needle and knit the stitch off it onto the righthand needle.) Continue on picking up sts up the right neck edge and on across the back.
Take it step by step and you'll get it to work. The picked up stitches always look better than you think they will. The video here is quite good but you can also try this one for a sweater neck