Grab some more arrows leaning against a rock on the other side of the stream. Then locate your first target: the skull totem (1/10) hanging from the tree near the overturned truck. If you're having trouble spotting it, just use Survival Instinct and it will light up.
Hold Aim (Right Mouse Button, L1 on PS3, L2 on PS4, LT on Xbox) to draw the bow. Now use the mouse or right stick to aim at the totem. When the targeting reticle turns red, you've got the totem in your sights. If you like, you can now press Z or click the right analog stick to zoom in. Adjust your aim if necessary to re-acquire the target.
Now, just to see how the charged shot works, hold the Fire button (Left Mouse Button, R1 on PS3, R2 on PS4, RT on Xbox) for a few seconds. You'll notice the red reticle now has a glowing circle around it, indicating your power shot is charging.
Release the Fire button to shoot. Bam! Or, to cancel a charged shot without firing, just release the Aim button.
When you've destroyed the totem, an on-screen message informs you that you've received 10 XP and unlocked a Challenge: Ghost Hunter, which you can complete for more XP. Check your map (Tab/Back). The box at the top right includes more information. You'll need to find and destroy 10 of these totems to complete the challenge.