Nothing happens after that. You just caught the three legendary roaming Pokemon in the Johto Region.
nothing, you just have three legendary Pokemon
Trade them from HeartGold and SoulSilver.
you have to find them again
You are stronger of cource by pecy Jackson
lugia, hooh, red garados but that doesnt really count, mewtwo, groudon, the three dog pokemon, the three bird pokemon, speacial event celebi,
You fight with them nothing special really happens
You don't, the three 'crown' Legendary Beasts are obtained via a wi-fi event for SoulSilver/HeartGold.
Groudon, Kyogre, and Rayquaza. Groudon is the fire legendary pokemon, Kyogre is the water legendary pokemon, and Rayquaza is the air legendary pokemon.
Between Mahogany Town and Lake of Rage.
After you catch them like any Pokemon they are saved on your pokedex and ready for use.
They are in both, so don't panic. :)
Yes you can.