It's okay to not know everything. First of all, it's pretty much impossible to know everything and once you did if you could, it would all change. So, it is okay to admit it: "I don't know much of anything about that . . ." That is a good thing, and even better is to add this phrase to that last statement: ". . . so I could use some help in that area." That's real progress!
CEO's of large corporations, like GM and Ford don't know everything about their own company, but they don't need to. It's not even their job to know everything. It's their job to lead and part of that leadership is finding the people in and out of the company who know what they need so they can call on it as needed. It would be a serious waste of time and talent for the CEO to know everything.
When it comes to small businesses, you may know a lot about the subject of the business that you run, but you can probably really use some help in marketing, web design, sales ideas and so on. There isn't any way that you could know all you need to know about everything either. So, admitting and accepting this and then seeking assistance is a very wise thing to do. Just by coming to this point and stating this will help the assistance to find you. There are lots of people and companies that are ready and waiting to assist you.