1) Assemble the battery: Remove the shrink wrap around the battery and insert the batteries in the right direction.
2) Insert the battery hold back into the bore sighter: As shown in the diagram below when the 2 points align the Bore sighter is on when they're not aligned its off.
3) Choose the right adapter for your barrel:
Choose the right adapter that fits your barrel and with the screwdriver tighten the screw into your adapter.
4) Insert bore sighter into barrel: Finally just insert the bore sighter into the barrel and make sure that the adapter is fixed in the barrel.