Align the corner of a panel at the intersection of the layout lines. Using a brad nailer, fasten it to the plywood every 6 inches along the edge. Angle the nails slightly. Don't nail any edges that need to overlap the next panel.
Ceiling panels have raised bubbles along their edges, which create a perfect ¼-inch overlap. Tuck the edge of the second panel under the first panel, lining up the bubbles.
Nail through two layers of metal at the bubbles. Continue nailing up panels in this manner.