Hi. It's probably a lot easier than you think. A business plan is just a way of writing down your idea.
You'll need to write a paragraph or two on each key topic eg what you want to do, where you will get the products from, why there is a gap in the market (eg who else is selling locally, what's available online, why people would use your shop), how you would staff the shop and explain how it will make money.
It helps if you can show this in numbers too, so try and create a monthly cash flow showing the turnover you are anticipating making, the costs of the product you will be selling, your staff costs, your fixed costs (rent, rates, power, phones etc) and the resulting profit. Sometimes you have to pay some costs upfront eg rent is typically 3mthly in advance so adjust costs to show when you pay them rather than a fair share through the year.
There are ways you might be able to get started and prove the idea without incurring a lost of expenditure. Another funding option might be to try peer-to peer lending sites such as Zopa and Funding Circle.