OK. am a Hyuuga nerd so i'll tell u a lot
The Byakugan is the primary focus of the Hyuuga's special arts. When the Byakugan is activated, their pupils become more distinct, and the veins near their temples bulge.
The first ability of the Byakugan gives the user a near 360? field of vision, except for one blind spot at the back of the neck above the third thoracic vertebra.
The second ability is having the ability to see through solid objects, and can use a degree of telescopic sight. The distance and the degree of telescopic sight varies from person to person.
However, the third and one of the greatest uses of the Byakugan is the ability to see chakra, as well as the chakra circulation system inside another's body. It is from this particular ability that they are able to employ their ultimate attack style: Gentle Fist. Unlike the Strong Fist, which is focused on external injuries, the Gentle Fist style focuses on internal injuries. Each strike, when placed correctly, strikes along the Chakra Pathway System, which is the network of vessels that carry chakra. This network is closely intertwined with the functioning of the body's organs, and so, when the keirakukei take damage, the organs suffer as well. There is no defense against the Gentle Fist, since one cannot train one's internal organs to become stronger. The only possible defense is to stop the Gentle Fist's hits from connecting.
Sometimes the users of Byakugan make some hand seals when activating the ability, though it is also able to activate without any seals. The used seals are: Horse, Tiger, Boar with nearly straightened fingers, Hare, Rat, Dog, Horse, Dog, Hare, Tiger with lifting just index fingers, Rat, Boar with nearly straightened fingers, Dog and Snake with the right index finger lifted straightly. Sometimes just the last seal is used, and most commonly no seals are used.
*activates byakugan*