Start with a provisional cast-on (black stitches at the base) and an even number of stitches.
Work some rows of stockinette (usually 3-4, but check your pattern).
For the picot break-line work [k2tog, yo] to the end of the row.
Then work the same number of stockinette rows as you did before the break-line.
To join the edges, start by removing the provisional cast-on and placing the cast-on edge stitches on a 2nd needle (same size or one size smaller).
Fold up the bottom edge so that the cast-on stitches are behind the active stitches.
Work the "joining row" by working k2tog - each k2tog is formed of one stitch from the front needle and one from the back needle:
Work to the end of the row - you should have the same number of stitches as the original cast-on.