Working class monsters
The only farm work your creatures can do are Harvesting and Watering. There unfortunately isn't a beast that can clear debris from your field, such as rocks and stumps. The creatures will only work on your farmland and can't take care of crops that you have growing inside of the caves.
To ask a monster to manage your field, simply talk to it and choose one of the two work options. The next day around 10:00 am they'll begin working. You will only have 1 Watering and 1 Harvesting beast out of the barns at a time, but you can assign multiple creatures to work. There's no advantage to hiring one specific type of worker over another one. The more Friend Points a monster has, the more efficient the beast is at its job.
Each creature will only work for around an hour and 40 minutes (about 80 squares) until it needs rest and automatically returns to the barn. If you have multiple creatures assigned to a task, the next one will start work on the hour mark. For example, if you had a Watering beast stop working at 11:40am, the next one will start at Noon and begin where the previous creature left off.
The beast will continue to work until you tell them otherwise. The Watering team won't leave the barn on rainy days, and the Harvesting team doesn't bother leaving if there's nothing to harvest. Neither one of them will work during the Winter season.
There are a few quirks with the working-class beasts. The Harvesting creatures will not harvest Fodder from mature Pasture Grass. Likewise, the Watering team will wet all tilled soil you have on your farm, whether you have crops planted on those spots or not.
If you want to take out a Riding monster, you'll have to ask it to accompany you out of its barn. To ride on its back, turn to the creature when you're outside together and press the A button. You'll then be prompted to hop on. Press A again to jump off the creature's back.
Controlling your direction is just the same as if you weren't riding. To make your creature run you only have to hold down the Left Shoulder button.
You can ride around the world but you can't ride in the village or into a house. Riding a monster does not make you immune to attacks while going through the caves. Both of you will take damage if you are hit by an aggressive creature. You can attack while riding by pressing the X and B buttons, but your friend's reaction time is so slow that he'll take more damage than if you just hopped off an attacked the enemies yourself.