Once you have created a new project, you need to select the video that you want to make interactive. It has to be hosted online (ie you cannot cannot upload a file to the Adways Studio directly). This video can be on YouTube or on your own server for example.
In the right column named project (if you do not see it, just click anywhere on the video area), you have to select the video source in a drop-down menu. Then you just copy and paste the video URL or the video ID.