Answer: Catch them in the wild by using a Pokeball.
All you have to do is walk into the grass that you find nearly everywhere and then you will enter a battle with a wild Pokemon. It is a good idea to lower their HP until you think it is weak enough to catch. Select 'Bag' and go into the Pokeball Pocket. Select the Pokeball you want to use. Hopefully, you will catch it and soon get the hang of it. Note: When in a battle against another Pokemon trainer, you cannot catch their Pokemon, they have already been caught!
Yes, You can catch Groudon in Pokemon Emerald.
You can't catch one in Pokemon Emerald.
No you cannot catch Entei in Pokemon Emerald.
You can't catch a Bellsprot in Pokemon Emerald. You trade it from Pokemon Leafgreen!
There are many Pokemon you catch that are similar in sapphire and emerald but there are many Pokemon emerald can only get and not sapphire.
Cressilia is a 4th generation Pokemon so you can't catch it in Pokemon Emerald.
You can't catch or obtain other trainers Pokemon in emerald.
No you cannot catch Celebi in Pokemon Emerald.
you cant. You can only catch it in Pokemon emerald, but, you cant catch latias in emerald.
You can onl catch LUNATONE in SAPPHIRE but you can catch solrock in emerald
imposible there is no such thing as bonsly in Pokemon emerald
You cannot catch Entie in Pokemon Emerald. You can catch Entie in FireRed, LeafGreen, HeartGold, and SoulSilver. You can trade Entie to Emerald from FireRed and LeafGreen.