working both sides on v neck

[LNKJ]

How do I work both sides at once? This is where I am at in the directions: Bind off 6 sts, work until there are 38 sts on RH needle, sl center 2 sts onto holder, join another ball of yarn and k to end. Work both sides at once.
Do I join another ball of yard to the RH or LH needle, and how do I work both sides at once. I'm sure it's easy, but I am a beginner and need some help. Thanks