hi there! welcome to the forum and welcome to the wonderful world of fiber arts!!! (cheesy, I know, but had to say it!)
assuming this pattern has you working the BOs on the right side only, which is typical, what it is telling you to do is bind of the 3 stitches on 1 RS row, then the next RS row, BO 2 sts, the next RS row, BO 2 sts, and then depending on what size you are making, you will then BO 1 st on the following 1, 2, or 3 RS rows.
I am not sure if that was your question, so I will elaborate a little further too. The neck edge will be the part closest to the 10 sts you bound off for the neck on each side, so on the right piece of the front, you will be binding off at the end of the row and on the left side of the front, you will be binding off at the beginning of row.
Also, when I say "RS," that is the right side of the work, meaning the "public" side, the part that will be out when you're wearing it.
To throw a monkey wrench in here, though, I am not sure why it's telling you to do them both at once. (That part, by the way, they are saying to do the right side of the front, drop that ball of yarn and do the left side of the front with the other ball, not sure if that was part of your question) the same time. Since you're adding a new ball of yarn anyway, you can work the right side of the front, finish it, and then work the left. The only time I wouldn't do this if it was with a handpainted or novelty yarn that changes frequently, because then it totally won't blend, but with a new ball of yarn anyway, you are going to run into that problem either way.
I am afraid I've either over-answered your question, missed it entirely, or confused you further, but please shout if I can clarify anything else for you!
Best of luck with it and just keep knitting, just keep knitting!