Hi! The word "job" is only a noun. It refers to someone's career or profession, something that they do every day, or some days a week, and get paid for. Some examples of it: "I have a job" - means I am employed "This is my job" - you can say this when telling or showing to someone what tasks or actions you do for your job, (so a teacher might say that explaining math to students is his job). This sentence could also be said with emphasis on MY, which someone might say if another person is doing a task that they are supposed to do. For example, if Joe is cleaning dishes, but the task of cleaning dishes was assigned to Tim, Tim might say "Cleaning dishes is MY job, not yours." Work can be a noun OR a verb. Like job, it can refer to a career or a profession, but it can also be more general, and is often used when talking about things that need to be done. Here are some examples: "I am at work" - here, "work" has the same meaning as "job". The person means that they are at the place where they go every day to do their profession and get paid. This is more common to hear than someone saying "I am at my job", but that would not be wrong either. "I have work to do" - This can be used for many things. It can be said to emphasize that you are busy, and cannot do something else because you have work that you need to do. Or it can emphasize that you have started a task or project, but you are not close to finishing it, so you have a lot of work on the project to do. This can apply to housework like cleaning or cooking, schoolwork (like studying or reading, sometimes also called "homework"), or the work at your career. Here is a good reference for more: https://www.espressoenglish.net/difference-between-job-work-and-career/

If you are sitting at your desk in your office, for example, the phrase you want is this: "I am at work". One key grammatical difference is that "work" is uncountable, while "job" is countable. Compare the structure of these sentences: I need a job. I need some work. I can't find a job. I can't find any work. There aren't many jobs in my city. There isn't much work in my city. The countable word "job" can refer to employment, in which case it's a single position, for example: "There's a job advertised in the Marketing Department. Why don't you apply for it?" or John left his job with AMC and got another one with a bigger company. It can also be a single task, for example: "Can you do a small job for me? I need someone to check these figures this afternoon". As 'job' is countable, it has a plural form - jobs - which refers to a number of separate positions ( or roles in a company) , or separate tasks to be done. Work, being uncountable, is more abstract. It's a part of your life ( usually separate from your home, your family or your hobbies), and it's something you need to do to pass exams or earn money. You can have a lot of work, or a little work, or no work at all. 'Work' isn't an individual thing ( like a job or a role) : it's 'stuff', like water, or love, or sleep, or happiness. I hope that helps.