Originating with the Ōtsutsuki Clan, the Byakugan is one of the "Three Great Dōjutsu" alongside the Sharingan and Rinnegan. They grant the bearer a near-360º field of vision around themselves, save for a small blindspot at the back of the neck above the first thoracic vertebra.
You can focus your vision on anything within the range of your Byakugan, and can penetrate nearly any object, being able to see through walls, underground, or even the contents of someone's body. You can see chakra to a greater extent than someone with a Sharingan, including the 361 tenketsu points along someone's chakra pathway.
The Byakugan's ability to see chakra grants increased resistance to falling under genjutsu, but doesn't completely remove the risk. They can, however, be used to increase the effectiveness of your own genjutsu.
These eyes operate without expending any energy, and suffer from no strain or fatigue from prolonged and uninterrupted use, wield them as you wish.