If you are talking about Virizion, Terrakion, and Cobalion, you have to first get to the point in your game where you can use HM03 Surf in order to surf over to the other side of the bridge in the northeast area of Route 6 (the season research lab), and on the other side of the bridge you will find a little bit of shoreline which leads to Mistralton cave.
Inside this cave, Cobalion will be waiting for you. Make your way through the cave and listen to the old man's story about the legendaries of Unova. Then, catch Cobalion. Once you do you will then be able to get to Virizion (which is in Pinwheel Forest on the northeast side of the long bridge) and then later on Terrakion (which is in the cave at Victory Road on the way to the Elite Four).
Only once you have the HM03 Surf and have caught Cobalion can you find the other two legendaries Virizion and Terrakion.
You are stronger of cource by pecy Jackson
You go to the three caves and catch them.
you catch 60 different Pokemon go to professor oak.catch mew and mewtwo catch one of the three legendary dogs. charmander...suicune bulbasour...entei legendary dogs to the left squirtle...raikou squirtle...raikou
Mespirit, Azelf, and Uxie are in the three lakesin sinnoh. Palkia (and possibly dialga) are in the end of mt. coronet.
No. They were made after Pokemon Yellow.
no
no.
try to catch your legendary. It varies on which legendary depending on what starter you chose.
a utra ball or a master ball
yes you can also catch them in soul silver.
you have to catch Palkia(in pearl)orDialga(in diamond)
grovile
You are stronger of cource by pecy Jackson
Strong Pokemon like lugia, ho-oh and the three legendary dogs
After you catch them like any Pokemon they are saved on your pokedex and ready for use.
You go to the three caves and catch them.
You don't, the three 'crown' Legendary Beasts are obtained via a wi-fi event for SoulSilver/HeartGold.