An online whiteboard is a kind of a platform, where you and your student can work on the same area simultaneously. You can draw there, write texts or upload images or exercises, so that both you and your students can see the changes.
There are different whiteboards, such as:
Twiddla is more complicated, but it gives you a wide variety of tools. According to recent changes, twiddla allows only 20 min. sessions for free. After that you will have to refresh the page (all the uploaded images will be saved in the library).
Awwapp is a simpler variant, but it works with mobile devices more correctly. It is easier to use will young students and allows free sessions with no limit.
Twiddla has always been more popular among the teachers. We created a tutorial to help you with using it at the lessons: