How to make posts on facebook public?

[pri✍]

Your question is how to post Public or how to share Public? it's two different things eventhough the basic is the same, the audience setting.

To Post to Public:
Before you hit Post, check & change the audience selector (at the bottom of status update box) to Public.

To Share to Public:
Before you hit Share, check & change the audience selector (at the bottom of status update box) to Public.

Just to remind you, your audience setting is stick, means unless you change it, it used the last setting for any future post/share.