The exp bar in the picture is your Rangeland, which represents a player's progression of Rangeland. As your level goes up, you can enhance your profit during milking and combat.
What are the benefits of getting your Farm level up?
Increase cattle's token yield in fighting and milking (check the yield chart above)
Unlock tech research of Tech Tree
Complete stall level achievement in Task to get rewards (daily tasks are not included)
How to raise Farm's level?
Unlock stall room (2 rooms provided by default; 8 stall rooms maximum)
Breed Cattle Mystery Box in breeding market +20 EXP
Grow a calf into an adult bull/cow +20 EXP
Use game items
Having a higher player/farm level can enhance your output when finishing a battle and staking