|Easy-breezy way: cut bias strip twice as wide as you need your top stitch, then add 1/4"x2 for seam allowance. Example: (1/4" topstitch x 2=1/2") (1/4" seam allowance x 2=1/2") = 1"....then add 1/8" because your bias is likely to get narrower as you handle it. So cut bias strips of 1 1/8" wide for a 1/4" topstitch.
Fold bias in half and set on to outside neckline. flip bias to inside, press and/or pin while shaping with hands for non-stretched out neckline. Basting is best until you've had lots of practice, or if your fabric is treacherous. You will have to experiment with what the best finish is for the ends of the bias, it depends on what shape neckline you are binding.
Hand finish with overcast stitch for discreet invisible finish, or topstitch from outside to keep even distance from edge. Use a cross-over catch-stitch on knits and it will have enough stretch for most knits, even if you use a woven bias such as chiffon.