By clicking on the globe mark under your Toot, you can set the privacy options for that submission.
Public（公開）: Toot will be displayed by all users on the Public Timeline.
Unlisted（非公開）: Toot won't be displayed on the Public Timelines, but it will be visible to all users.
Followers-only（未収載）: only followers can see the Toot.
Direct（ダイレクト）: only certain users can see the Toot.
*Privacy settings might fail to be applied in poor connection environments and according to the app version.