Far and away the best prize that life has to offer is the chance to work hard at work worth doing. Theodore Roosevelt, 26th President of the USA.
People are often puzzled with how to say posao and zanimanje in English. The easiest way is to refer to everything as ‘job’. But English has much more to offer.
A job (countable noun) is the regular paid work that you do for an employer, especially when you work for a company or public organization. A friend of mine told me his last job was with a computer firm and his current job is in advertising. But, he would like a job in TV. Are there any jobs (not work or works) in TV? He might apply for a job there. It might be hard to get a job (or find a job) there or hold down a job (keep a job when this is difficult).
Work (uncountable noun) is used in a more general way to talk about activities you do to earn money, either working for a company or for yourself (like employment). This friend of mine started work when he was eighteen. People who are employed are in work (have a job). However, there are people out of work (without a job). They are looking for work, but they have difficulties finding work. Another friend of mine is returning to work (start a job again after a while) after being on a maternity leave. You should try to avoid questions such as What is your job? or What is your work?, but say What do you do (for a living)? Be also aware that you usually have a lot of work to do when you are busy, and not a lot of job.
Post and position (countable nouns) are more formal words for a job in a company or organization, used especially in job advertisements and when you are talking about someone moving to a different job, e.g. This post would suit a recent graduate. They need to fill a post, because Mr Smith left his $50,000 a year post in July. He has left for a teaching position (or post) in Germany. He will take up (start) his new position in June.
Vacancy (countable noun) refers to an empty position, e.g. We have no vacancies for photographers at the moment. However, it can also refer to empty rooms in a hotel where you often see signs No vacancies (no free rooms available).