To sterilise your jars simply wash them (together with lids) in hot soapy water and dry stood up on a clean baking tray in the oven preheated to 150°C/300F for 10-15 min. The jars should be straight from the oven when you pour in your hot orange marmalade. Alternatively, pop them on a hot dishwasher cycle but time it right so that they're ready when marmalade is.