You may need to get a workshop manual because as you assemble the timing chain and sprockets, there might be pre-alignment procedures---I don't know how much of the engine you've taken apart, so that may or may not apply.
But I'll get you started:
Rotate the crankshaft so that the following conditions are met:
- The number 1 (front most) cylinder is at the Top Dead Center (TDC) position.
- The keyway on the crankshaft (5) aligns with the mark on the engine block (4).
- The arrow (3) on the idler sprocket is pointing upward.
- The guide pins (1) on the camshaft sprockets line up with the notches (6) on the cylinder head.
NOTE: The timing chains need to be aligned to specific locations during assembly. Refer to procedure for further information.