Shape Neck

i am working on a Vest. The Vest Right front has border and I have completed the pattern 12" as asked, but now they are asking to shape neck and i do not understand how.
I have 52 sts and for neck shape:
RS: K3, ssk, work in pat to end. Dec 1 st at next edge inside garter border as set every other row 15 more times.

I do not understand how to do this, can some one help me step by step?

I’m assuming that the border is the k3? In that case, on each right-side row you’d work the [I]k3, ssk, work to end of row[/I] a total of 16 times. The k2, ssk [I]is[/I] the decrease inside the border.

That first row sets it up for you - k3 is the border, then you ssk next and that’s the decrease inside the border. So every RS row, that’s how you do it.