Use pokeballs.
no.but you can trade it who someone who has it at firered leafgreen and yellow version......
if you want to cheat to get all legendary Pokemon on ruby you have to play on the computer
This legendary Pokemon can only be acquired on Ruby Version through trade from Sapphire Version or Emerald Version.
Ground
You can't catch a sentret in Ruby version, but you can catch one in Emerald version.
groudon but in a updated version.
You battle it and you choose whether to catch it or not.
you can catch groudon in ruby in cave of origin then beat the elite four to catch rayquaza on sky pillar
After Latios comes Kyogre, the legendary Pokemon for Sapphire Version.
You can't.You have to trade it from Pokemon Ruby Version
just weaken it to the red and throw ultra balls
I am sorry to say this but, you cant catch any of the Pokemon in platinum in ruby unless it is a hoenn Pokemon.