Well t find Groudon follow the sory you wll see team Magma trying to make more land by summoning Grodoun
When you meet groudon you could do a few things

#1
first save before encountering
then battle and use a mastrball
and you are done
#2 First battle and use masterball
and you ar done
#3 Save before battling battle and weaken groudon
then use any ball
#4 save before battling
then battle groudon and weaken it and then give it a status problem either Sleep Frozen or paralyzed
then throw a ball at it any ball will work if you are lucky

and that is how you catch Grodon the choice is yours number 1 - 4