They are still in Beta and you need an invitation code, which I got in my email immediately after I requested it.
It’s very straightforward to record your screen there following the instructions. The audio you record after you’ve captured the screen, which feels a little awkward, but it’s manageable after some practice. You can also add subtitles after having captured the screen.
Then, it’s just a matter of publishing it and getting the embeddable code.
All in all, screentoaster is a nice free option to prepare tutorials, show specific collections of pages and adding voice comment.