In Chinese, we could hear people tell us "加油" in many situations, like when we decide to do something, have to pass some test or have to win a competition. It is a kind of words to encourage somebody.
"Oh, man... I have to do overtime tonight."~~~"加油"
"I worry about the exam tomorrow."~~~"I am sure you will pass the test, 加油"
"I like that girl, should I tell her?"~~~ "Of course, just tell her how you feel, 加油"
But it is hard to find the real translation in English. The real translation in "加油" is to fuel up gasoline. It is quite different meaning in Chinese. Indeed, we really use "加油" , when we refuel the vehicle, but we used in encouraging others more often.