Catch what? MissingNo.? It's just like any regular pokemon. I've not tried catching it in a while as I did lose a game to it, (not a cart), but it's just like any regular pokemon, get it to sleep or paralyzed before you try and catch it, which I don't recommend.
Could you please restate your post in a way that isn't stupid, dumb, or idiotic? -screwydude