The sides of the dart are called dart legs. They are marked on the fabric when it is cut, see "Cutting Fabric". To sew the dart, fold it in half placing one dart leg on top of the other, then pin the fabric. Look at both sides of the fabric to make sure the pin is going through both dart legs.
Fold the dart along the dart center line.
Pin the legs of the dart looking at both sides to make sure the pin is going through both legs.
Start sewing the dart at the top with three or four reverse stitches.
Sew to the point of the dart, keeping the last two or three stitches parallel to the center line.
Remove the fabric from the machine leaving at least 3" (8cm) of thread beyond the point. Tie three overhand knots over the point.