Autosaving works in the background while you are making a post.
This means all the content in your post will be saved automatically in real-time. If you get interrupted and need to come back later, feel free! You can also start a post on your computer and pick it up on your mobile device if you need to - and never miss a beat.
If you no longer want to keep a draft of that post, simply click the Discard button ---> that draft will be deleted and you can start fresh with a new post.