What is different between these words?
All of these words mean job in English but when to use them?
Even if they might all be translated to job in English, they don't mean the same thing in French.
job is used as emploi or travail. If you are unemployed and looking for a job, you can say je cherche un emploi or je cherche un job or je cherche du travail.
métier is most of time what you learn. If you learned engineering in a school, you can say j'ai appris le métier d'ingénieur
profession is the title or a group of métier. If you are a nurse, you can say je travaille dans une profession médicale. profession is closer (synonym) to métier.