You will be billed every quarter for all the electricity and gas you have used in the business.
Until you have been trading for a few months you will not know exactly how much energy the business will use. You could contact your energy supplier who may be able to give you an idea of likely consumption, based on the area of your premises, your opening hours and the services you provide. You can adjust the figures once you have been in the premises for a few 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.
Energy prices are high and seem very likely to keep on rising in future, so it makes good sense to include efficiency measures when you fit out and equip your premises.