When you enter the farm, there is a Chocobo standing next to the pen fence. Talk to it and reply ‘Wark’ and the Chocobo’s will dance :). Afterwards you’ll recieve the Choco/Mog materia. Go into the house on the left and talk to the guy here. You can rest in the room with the beds fro 100 Gil. Go into the barn on the right and talk to the kid in here (Choco Billy). From him, you can learn how to catch a Chocobo, but eventually you will need to pick the bottom option and buy a Chocobo Lure off him for 2000 Gil. You should probably buy some Greens off him as well. Go out of the farm and equip someone with the Chocobo Lure. There are Chocobo tracks outside the farm on the lighter grass. Catch a chocobo by wandering around on the tracks until you enter a battle with a Chocobo and other enemies. You must never attack the Chocobo or it will run away so don’t attack with magic paired with All. You will need to kill the enemies quickly or the Chocobo will get scared and run off. If you bought Greens you should throw them to the Chocobo by selecting them off the Item list. This will distract them while you attack the enemies. When you have killed all the enemies and the Chocobo is still there, you will have caught the Chocobo. After the battle you will be riding the Chocobo on the World Map.
There is a marsh near the Chocobo farm, look around with the camera to see it, it looks grey and green. Use the Chocobo to cross the marsh and avoid the large snake in the marsh, the Midgar Zolem. If the snake does touch your Chocobo you will have to fight it. I strongly suggest trying to avoid the snake as it is very tough at this stage in the game. If you really want to fight it here’s a strategy for it (but you have to cross with a Chocobo first:
As soon as you leave Kalm, make a group with Cloud, Aeris and Barret. Go to Chocobo Farm and get the Chocobo Lure Materia with Choco Billy. Leave the Farm, capture a wild chocobo and cross the swamp, but don’t touch the Snake. Enter Mithryl Cave and go to a room to the right, where you find a enemy called Ark Dragon. You can steal some Ether from it, which is very rare at the beginning of the game, and they are worth plenty of money if you want to sell them. This enemy has a attack called Flame Thrower, which can be learned, and the best, makes your Limit Break gauge fill up as crazy, being easier to gain more Limits this way. Fight until you reach level 20-25, and have the Limit Break Lv. 3 of Cloud, Aeris and Barret at full. Save the game, and go face the Midgar Zolom. Leave the Enemy Skill Materia with Aeris, and the first attack should be made by Cloud or Barret. When the monster removes one of your characters from the battle, use Aeris’ Limit Break Planet Protector, which will make your group invincible. When the monster is very weak, It will use Beta, which can be learned. After learning the magic, discharge Cloud’s Meteorain or Barret’s Ungarmax, this should finish with the Midgar Zolom. Now you’ve defeated the strongest monster until this point, and got Beta, one of the strongest magic in the whole game.
Either way you will get to the other side of the marsh; ride into the cave on your Chocobo, you will see a large snake on a spike. Go north, dismount and enter the cave.