If you're talking about the front of a sweater vest, you knit to two stitches before the center stitch, Knit 2 together, put the center stitch on a safety pin to hold it for the neckline edging, turn your work and purl back to the armhole.
Usually the neck edge decreases are done on the right side every other row, until you get to a specified number of stitches left, then do any shoulder shaping. Your pattern may have different instructions.
You work the left side of the front first, then go back, join another strand of yarn for the right side of the front and work up to the other shoulder reversing the shaping.
If you have questions about the directions in a specific pattern, it would be helpful to have a link to the pattern, or write out the particular instruction you're having trouble with.
Good luck and Happy Knitting :XX: :XX: