When exploring Seirai Island, just like all other regions in Teyvat, you will encounter dozens of puzzles to make your time in-game worthwhile.
In Koseki Village—an area in Seirai Island of Inazuma—when you go up the hill south of the little residential area, you will find a couple of Discharge Stones and Relay Stones scattered in the area. A Cumulation Stone is located at the center of the area where these objects are situated.
This puzzle aims to link the stones or relay the Electric current from the Discharge Stones to the Cumulation Stone at the Center.
Specters will randomly appear and attack when you explore the area, so before solving the puzzle, make sure you have gotten rid of said monsters.
Since this is a Relay puzzle, Relay Stones should be around for you to use.
If you check the surrounding area of each Discharge Stone, you will most likely find one Relay Stone.
Take each Relay Stone and place it between the Discharge Stone and the Cumulation Stone.
Do this to all three Discharge Stone to solve the puzzle and get your reward.