Different appliances use different gases. Your manual should state whether the appliance runs on 'Butane' or 'Propane'. As a rough guide, Propane is more often used for cooking or large-space heating applications and is generally used outdoors. Butane is better for indoor appliances such as Cabinet Heaters which are used to warm your house.
Sometimes it is the appliance regulator (the part which connects to the cylinder) that will tell you which gas the appliance takes. We have 'Calor Gas' chooser on our website which takes you through the steps to enable you to know which product is required.
You can visit our Calor Gas chooser by clicking here.