When you Publish a post, it gets added to https://write.as, where you can easily share it. Each post has a unique URL (like write.as/p2ss6e79etmvh) which only you have access to until you share it with someone else. If you don't Publish a post, it remains stored on your phone or tablet.
You retain ownership of any content you post to Write.as. By posting on Write.as, you simply license us to distribute the content around the world, that is, make it available on the internet. You will always control who your content is shared with, as only you know the unique URLs of your posts. Unlike many other services, your posts are unlisted by default, and we have no plans to change this.
All of your data is sent to the Write.as servers encrypted, which prevents anyone from eavesdropping on what you post. If you want even more security, you can enable the Always use Tor setting in the Android app, or add the --tor flag from the command-line and further anonymize your actions.