Assuming you've engaged your audience with the Executive Summary then readers will want to plunge straight into a description of your planned product or service offering(s).
This is the place to flesh out what you propose to do for customers and how you'll do it. Remember, it doesn't have to be a 'new wheel' - the people who brought McDonalds and Starbucks to new countries built on the shoulders of those who'd pioneered the models in America; they didn't have to invent the entire concept from scratch. But your product or service absolutely does have to meet a felt need in the market you're intending to address. You'll explore the size and nature of that market in a later section of the business Plan.
For now, describe enough of the product and service to identify what you're going to do and to give evidence that you know how you're going to do it: what you already can do, and how you're going to develop it as time goes by. This last point is very important because markets and technologies don't stand still. Something that might be right to sell now will need to develop and change as time goes by and it's important to show some initial appreciation of things you might want to do to develop your position.
Rest easy, though, that the Business Plan is meant to be a living document that changes over time and you will put flesh on those bones when the time is right. For now, readers of the plan will want to know your thoughts about how things might unfold.