I guess, you pulled the head to replace the head gasket or do other work.

Basically,
-get piston #1 to top-dead-center (TDC, top of the stroke; there's also a red tick mark on the main pulley and a gun sight the points to it on the front of the engine)
-look at the cam sprocket (there should be an arrow pointing out from the center near one edge, and two tick marks +90 and -90 degrees)
-the arrow should point up 90 degrees to the head gasket surface
-the two tick marks should be parallel to the head gasket surface