Farmhands are amazing in Farm Together, and when you hire a farmhand, they will work on a 13x13 square area on your farm. In this area they will tend to any crop that is planted there, as well as tend to picking trees, watering flowers, feed animals, and harvest flowers that are ready.
In order to get farmhands, you first need to reach level 20 to build the Farmhand building. You can buy this by pressing space to open the shop, and just scroll down to the Farmhand building.
You buy farmhands per hour, and the price is 2x Tickets per hour. You can only hire each farmhand for 4 hours at a time, which is real life time that only counts when you actually play the game. So you won't have to worry about them very often.