A webinar is the abbreviation of Web Seminar. This means that you can simply log on to a special webpage (the address is provided to paid-up participants before the event) where you are connected to a special platform.
It is LIVE because the tutor is presenting methods and information in a live broadcast that you can immediately see and hear on your computer screen and speakers.
When he turns a page on his presentation, it is shown on your screen. When he asks you to answer a question or a poll, you can chat LIVE or click on a button to provide feedback - making it a fully interactive experience.