These smoking devices heat liquid nicotine to create a vapor. You inhale this vapor into your lungs. Nicotine in the vapor enters your bloodstream. It stimulates your body, activating reward circuits in your brain.
Why do people use e-cigs? Well, some believe e-cigs help people quit smoking. They are sold as a safer alternative to tobacco. Research does suggest they're less harmful than cigarettes. But we still don't know about the long-term effects on your health.
One issue with e-cigs is their use by people who have never smoked cigarettes. Because nicotine is highly addictive, new users get hooked. And once you're hooked on e-cigs, you may find yourself using them more and more frequently.
The best choice is to never use nicotine in any form. If you are addicted to e-cigs, talk to your doctor about how you can quit. Nicotine is a hard habit to break. But with patience and effort, you can do it.