How do you use Black Luster Ritual in Yu-Gi-Oh?

Answer 1

Answer taken from the Official English Rulebook: When you have a Ritual Spell Card, along with the matching Ritual Monster Card, in your hand, along with the required Tribute (as listed on the Ritual Spell Card), you can activate the Ritual Spell Card, placing it in the Spell & Trap Card Zone. If the activation of the Ritual Spell Card is successful, Tribute monsters by sending them from your hand or the field to the Graveyard. The Ritual Spell Card will list the required amount to Tribute. After sending the Tributed Monsters to the Graveyard, play the Ritual Monster Card onto the field in either face-up Attack or Defense Position. Finally, place the Ritual Spell Card in the Graveyard. In your case, "Black Luster Ritual" would be activated once you have "Black Luster Solider" in your hand. Now you pick monsters (other than "Black Luster Solider", of course) that are on your field or hand and send them to the Graveyard. The stars of the monsters that you select must total up to 8 or more in order to Ritual Summon the 8-star "Black Luster Solider". Then you Summon "Black Luster Solider" from your hand; this is treated as a Special Summon so you can Normal Summon or Set another monster that same turn.

Answer 2

Gaia the fierce knight, Dark Magician and Kuriboh on the field... then activate the ritual