To create a draft post, you have two options: toggle “This is a draft” in the Publishing Composer.
You can also create a draft post directly from the Draft Library (in Library > Drafts).
This is also where you can access your draft posts.
Note: Draft posts will never be scheduled, even if a date has been set.
You can save a post as a draft at any time in your process: before adding accounts, before adding media, or before adding a scheduling date.
If you add a scheduling date, the draft will appear in the calendar and can be filtered.
If no date has been set, along with all other drafts created, then it can be found in the Draft Library.