During your Main Phase: You can send the top 2 cards of your Deck to the Graveyard, then if any "Lightsworn" monsters were sent to the Graveyard by this effect, this card gains 200 ATK until the end of your opponent's turn. You can only use this effect of "Raiden, Hand of the Lightsworn" once per turn. Once per turn, during your End Phase: Send the top 2 cards of your Deck to the Graveyard.
Because Raiden can mill during your Main Phase, this let you Special Summon Wulf, Lightsworn Beast and let you make a level-8 Synchro. Lumina Lightsworn Summoner can revive Raiden to make a level-7 Synchro.
Here are some of the cards you want to use alongside your Lightsworn monsters. Raiden has 2 effects that mill cards from your deck every turn helping Realm of Light and Lightsworn Sanctuary gather counters.