You gain access to your farm when you occupy your city. You start with 3 plots of land and gain an extra spot every 5 farm levels up to a current maximum of 9 plots. Every 5 levels you also unlock more crops that you can plant. Currently only level 1 and 2 1hr and 4hrs crops can be purchased using gold, higher level crops and 12hr crops must be acquired using balens, from VIP wheel spins or as rewards from events.
The main crops available are Daru, Kyanite, Gold and Experience crops. There are other "special" plants such as voucher or insignia, or "event" plants such as pumpkins.
To increase your farm level you need to gain farm experience. This can be done in 2 ways:
1. You can weed, exterminate pests and energise the trees of friends' farms. Each plot weeded or pest exterminated is 1xp; xp from energising trees depends on friendship level. Energising tree s also increases your friendship with that person. You can only gain 200 xp per day by "helping" friends. This resets at 0:00 PST daily.
2. You can weed and clear pests from your own farm.
Please note: your farm level CANNOT exceed your player level
When you reach a level 30 farm you can start to upgrade your farm lands. You can use either balens or vouchers to do this. Vouchers are easily obtainable in game so are usually preferable. Each land upgrade increases the yield and decreases the time frame for the crops to ready.
You can also use balens to speed up the crops being ready. This halves the time left on the clock for them to finish.
You can also used the farming system to "steal" your friends' crops. When someone's crops are ready their crops become available for everyone on their friends list to harvest until the farm owner harvests them his/her-self. Each time you harvest a friend's crops you decrease their yield by 10% of what they have left, as that is the amount you take.
Up to three friends can harvest one plot.
Generally speaking, 1 hr crops are not worth stealing, 4 hr crops are preferable. Higher grade/balens/special crops are highly desirable steals but may result in upsetting your friends so tread carefully.
Camping farms until their crops are ready is considered bad form and rude (although i make an exception for one person
they know who they are ^^) and is highly likely to result in you being removed from a farm friends list.
Each person has their own opinion about the stealing system, some people welcome it while others frown about it. Be open minded, have fun, and don't be offended if you are stolen from or have been removed due to stealing.
Good luck and enjoy the game!
Edit: Also note that if you have pests and weeds on your crops when they mature that also reduces your yeild by 10% per pest/weed. Your crops will still be open for 3 steals after this initial reduction of yield, meaning potentially you can lose as much as 41-42% of your crops if the circumstances fit.