Okay, I don't know exactly where it is, but type in Pokemon Walkthrough 6 platinum in Google. The first or second site that comes up click on. It will have a list of a complete walkthrough of a part of the game. In this walkthrough (if you scroll down) you will see a Mt. Coronet checklist. Scroll a little more down, and you will get complete instructions on how to get to mt coronet. Along the way, you will encounter Galactic Grunts who are not hard at all. Finally, once you reach spear pillar, there will be two grunts who you have to battle 2 vs. 2. Then, (try to heal before upcoming battle) you and your rival will have to battle Commander Mars and Saturn. After you beat them. You will see Cyrus summoning Palkia and Dialga. Then you see Giratina in a shadow form. Cyrus goes into the Distortion World (where Giratina lives) and Cynthia comes and asks you if you want to go to the Distortion world. Say yes, and proceed. Then, the Pokemon Walkthrough 6 will also give you info on how to reach Cyrus in the Distortion World. Once you find him, you battle him and should win (pokemon should be high 40s or low 50s). Then, Cynthia comes to congratulate you, but you can also catch Giratina. I suggest to use the Masterball Cyrus gave you after you beat him at Veilstone. Good luck!
Sorry this was so long.
Cyrus
go to the spear pillar
on the top of mt. cornet with cyrus.
you have to go to mt cornet and there is palkia and Cyrus
mt. cornet
you go to mt cornet
you find Cyrus in celestic town. you find Cyrus in celestic town
I think he goes straight to Mt Cornet.
you can find Cyrus at the top of mt cornet at spire pillar when you first appear out of the cave.
in mt cornet in mt cornet
you go to the oroburg entrince to mt cornet and use rck clime
pass mt cornet to the top of the mountain where there is mesperit, azelf, uxie, and plkia