Simply hold the heater onto your mug to submerge, plug it in, unplug when it reaches your desired temperature, wait 15 seconds, then remove from liquid. Super lightweight and prefect for travel and car use. The heater fits into any car's 12V cigarette lighter socket. Quickly boil 500ml liquids in about 10 minutes. Great for heating up water, tea coffee, soup broths and much more on the go. Small enough to fit in your pocket, these travel-sized immersion heaters are a fantastic space-saver. Note: Only use on thin liquids that have the consistency of water. Always keep heaters submerged before plugin and unplugging or else safety fuse will burn out.