You will be billed every quarter for all the gas and electricity you have used in the business.
Until you have been trading for a few months you will not know exactly how much energy the your shop will use. Your various machines will all use different amounts of energy and you may find this difficult to predict until you have been using them for a while although you may find that machine manufacturers will be able to give you an idea of energy consumption. You may find that you will have to revise your heat and light figures after a couple of months.
It's worth shopping around the different energy companies to get the best deal for your business, particularly if you're going to be a heavy energy user.