The berry pots are for planting berries. By planting berries you can grow more of them. Just be sure to water them regularly, and pick them as soon as the plant bears fruit, or else it might wither before you get the chance.
you get them by talking to someone in goldenrod city
Actually it depends how how much you care for it and for what type of berry it is.
you give them to the guy that says shard de berry and he gives you berry's for them
If you already have the berry pots and some sense of time you can grow them really easy. If not the best place is to use the Pokewalker to get shards and trade with the juggler in violet city next to the Pokemon center
you pour water on it from a squirtbottle you get for watering the berry pots. you get it from the woman in the plant shop next to the gym in goldenrod, if you have the gym bagdge you will get the squirtbottle
sorry you have to trade it to Pokemon soul silver
Soul silver is AWESOMENESS!! yes GET IT
you cant unless the Pokemon has refresh or a berry that heals a burn or it has natural cure(only works if they switch out the Pokemon with the ability natural cure).
According to Serebii.net there are 493 Pokemon in Soul Silver.
yes you can plant berries using the berry planter, only 4 spaces each time
You can't do Pokemon contests in Pokemon soul silver.
Why Soul Silver is about the original Pokemon Silver game for game boy. Soul Silver has some more bonuses.