I think I'll need a little more detail before I answer your question with any kind of specifics. I'm unsure if the question is about what the businesses main responsibilities are what an employees main responsibility are at the business?
The responsibility of the business can differ by size, industry, and classification (DBA, LLC, Corp, etc). That said the main responsibility of the business is typically to be profitable. Without profit, the business can't survive, employees don't get paid, vendors and landlords don't get paid, and the business collapses. Secondarily they typically have the responsibility to be fiscally responsible, ethical, law abiding (license & certification compliance, not bribing, environmental, various other laws) and socially aware and responsible.
The main responsibility of an employee at a business vary's widely by business, industry, leadership, culture, position within the company, etc.
Hope that helps. I recommend refining the question so we can better answer. :) What I typically do is:
1) identify my question
2) before asking, I then think about what specifically I want to know - this help me boil the question down, making it more succinct which makes it easier for the person answering to answer more specifically and for you to get the answer you're after sooner.
3) I ask the question in very specific way.