To trade you will need two gamepacks and two Gameboys. Hook up the Gamelink Cable to the Gameboys and go to the starting menu where you can choose to start a new game, continue, copy, erase, or trade. Select "trade" and then choose which saved game you want to trade with. After that the game will save and you'll reach the trading menu.
If all goes well you'll be able to select one of the 6 different ways to trade with your friend. If you receive a message saying that the game can't find your Partner then activate the trade option from the main menu and try again.
Trading Animals - You can trade young and adult animals. When you select an animal its name, condition, and gender appears at the bottom. Its love level will appear in the middle of the screen. Love levels are scaled between 01 and 99, so if you see an animal with a love level of 62, you know it has a total of 6 hearts.
Any animal you trade will have its love level reset to 01!
So if you trade an adult cow that is giving large milk (love level 82) then the traded cow will only give small milk (love level 01) the next day. The only exception are Golden Chickens, who will loose their love level like all other animals but will still give Golden Eggs as though they had a love level of 99.
If you are trying to trade an animal and your friend doesn't have room for it in the barn then you'll receive a message saying so. You also can't trade animals that are pregnant. You'll always be asked to accept the trade before the animal is actually traded. After you accept the animal is traded, your new animal's icon appears in your screen, and your game is saved.
Giving an Animal - If you want to just trade 1 animal to your friend then select this. Your friend will be asked if he/she wants the gift; accept to continue. Select the animal you want to give and have your friend accept the gift.
Trading Seeds - You can trade one bag of seeds at a time. Pick the seeds you want to trade and accept the prompts.
Giving Seeds - Same as trading seeds but you give seeds to your friend.
Trading Tools - If you want to trade tools select this. You can't trade the Hoe, Sickle, Shovel, Watering Can, or Ax. You can trade all of the other types of tools though. You can even trade the machines you use to make Mayonnaise, Butter, Cheese, Knit, and Yarn!
Giving Tools - Instead of trading a tool for a tool you can give one to your friend. Select which tool you want to give him/her and have your friend accept the trade.
In fact the only way to get the girl partner (if you're playing the boy version) to take care of the sheep is to trade the Shampoo from a girl version to a boy version. After that when you ask your girl partner to take care of the animals or do "anything", she will take care of the sheep instead of telling you she took care of 0 animals. Don't worry about the lack of Shampoo in the girl game you got it from, because she can go to the Farmer's Union and buy a new bottle for 800 G. You can also trade the Miracle Glove from a boy version to the girl version if you wanted to. Then your girl game can pick produce without having to run back and forth to empty the rucksack.
Exit - Leave the trading menu and return to the title screen.