If you want to know more about how a timeline works, maybe it would be beneficiary to look at a few tutorials of pretty much ANY animation software like After Effects, Adobe Animate or Moho.
The exciting thing about the timeline is, that you can do your tweening animations inside the layout editor and see an instant preview. You can add multiple timelines so my guess is you can make like different timelines for like i.e. a sprite floating into the screen and one when it floats out of the screen and then call upon them via code. What's also neat is that the keyframes seem to have indexes so i certainly hope there will be a way where we can call upon actions to happen on specific keyframes within a timeline.
It's kind of the early Flash/Macromedia Director way of doing interactions. You should be able to animate pretty much any property such as scale, position, opacity etc. and just do it in a much more intuitive way than to code it, test it, see that it looks wrong, change the code, test again, etc.
Currently it's really just an experimental feature and i couldn't get it to work. It still needs some usability iterations and, of course, bug fixes until it's fully functional but i think it's a great addition to make C3 even more powerful. Whether you want to use it or not is, of course, entirely up to you in the end :)