There are two ways to use night vision in Ark: through the use of a headlight, or by using special goggles.
Headlights can be found in any supply drop and can be equipped in your hotbar. Once you have a headlight equipped, simply look in the direction you want to see and hold down the left mouse button. Your view will switch to night vision mode, allowing you to see in the dark. Be aware that headlights do not last forever and will eventually need to be replaced.
Goggles can also be used for night vision, but require you to craft them first. The recipe for goggles can be found in your survivor's inventory under the crafting tab. To craft goggles, you'll need 1x lens, 2x hide, and 3x fiber. Once crafted, equip the goggles in your hotbar and press the left mouse button to activate them. Goggles provide unlimited night vision as long as they are equipped.