1. “打工” only came into the inland China( 中国内地 [* Note]) decades ago from Hongkong (where meaning 'working as an employee), therefore bearing a strong vernacular feature, but it has become a common word today. 2. 打工 has all but taken the place of 做工, which has the same meaing and was commonly used before 打工 3. 打工 is used in the inland China today in two situations: A. to work as a laborer to earn wages 村里的大部分年轻人都到大城市打工去了。 B. to work for the propietor's gains, and earn a mere 'hardwork pay' for themselves 给别人打工 美元让全世界都在给美国人打工/美元让全世界都成了美国人的打工仔 （打工仔：young laborer, of the same origin） * Note: inland China: 中国内地 1）geopolitically, the part of China apart from Taiwan, Hongkong and Macau 2）geologically，the part of China away from the coast mainland China: （中国）大陆 1) geopolitically， the part of China apart from Taiwan, relative to Taiwan 2) economically, and occasionally, the part of China relative to Taiwan, Hongkong and Macau，but 内地 is normally used in this case

打工 : means this person works temporarily, probably part-time, at a place where doesn't require a degree. 他哥哥在一个中学打工。Sounds like he is working at the cafeteria or at the library of that school. 工作： Any other formal jobs. If you say 他哥哥在一个中学工作，I would think he's probably a teacher of that school..

HI，sounds to me that 打工 is more like either you were still a student during the job period and also like the job is not that fancy, while 工作 is more formal when you graduate then you find a job. And I am not sure about the second half of the sentence. I can't understand 弟弟在南旅行。

这么说吧，所有的职业都叫“工作，”所有的“打工”都属于工作，就像“北京”属于“中国”一样。 “打工”的意思就是，自己做的这份工作，自己不是老板。

打工：1.do a job that doesn't need high degree and usually get low salary,and usually it is a part-time job ,for example :（他不想问爸妈要钱，周末就在学校图书馆打工挣钱。and your sentence should be this kind of situation ) ；他没读过几年书，初中毕业就去广东打工了。 2. work as a stuff ,not as a boss , 我不想为别人打工一辈子，我想自己当老板。

工作：do a formal job ,我哥哥在学校工作。he might work as a teacher ,or some regular jobs.