Where do you catch all the legendaries?
Palkia and Dialga are found in the spear pillar when the player has obtained the lustrous orb for palkia and the adamant orb for dialga. Both ar level 47. The griseous orb looks like a gold nugget.
Giratina is found in the distortion world and turn back cave. Giratina is level 70 and to get giratina's origin form, in turn back cave where there is a portal, go inside and keep on walking and there is an item near the end where distortion world is. It is a Griseous orb that looks like a gold nugget.
Uxie can be found in Acuity cavern, Azelf is found in Valor cavern and mesprit is found in Verity cavern but will roam sinnoh when met.
Regirock- Desert Ruins (In Emerald)
Regice- Island Cave [Route 105 (In Emerald)]
Registeel- Ancient Tomb [ Route 120 (In Emerald)]
Regigigas- Beat elite four then enter snowpoint temple and find statue awaken if found all 3 regis at last floor.
Cresselia- Go to Canalave city to sailor edrich's house. Talk to little boy. Then set sail to full moon island and find cresselia where she will roam and leave a rainbow wing for boy. You will have to track her with marking map just like Mesprit.
Heatran- When you have defeated team galactic for good, go to stark mountain and you will find him there.
Shaymin- Obtainable in route 224 when obtained oak's letter
Manaphy- Hatch from egg from ranger.
Darkrai- Full moon island when obtained member card (Found on Newmoon Island)
Phione- Breed ditto and manaphy to get phione egg
Arceus- get azure flute and play in spear pillar to reveal the hall of origin where arceus is.
Zapdos, Moltres, Articuno- Roaming Sinnoh after obtaining national pokedex
Hope i helped! :)