It depends if you are nailing it horizontally or vertically. For Vertical installation you will need to nail some blocking horizontally across the wall so that you will have some thing to nail to.

Before nailing the boards in place measure make sure that that you don't end up with too small a piece of board on one end. If necessary trim the first board so that it will be the same width as the last board (approx). Nail the first board down on both edges start by placing the sawn side or groove towards the edge of the abutting surface. Nail through the tongue diagonally. Continue by placing subsequent boards on top of the tonques and nailing through the tongue again..... The last board will simply be nailed on the grooved side (sawn) with finish nails.