You have to first make sure the post can be shareable if you want people to share whatever you post on your Facebook page. You need to make your post public if you want your friends to share it. Follow these steps for how to make a facebook post shareable:

The "What's on your mind?" section can be seen on your Facebook home page.

The "privacy dropdown menu" will appear under your Facebook profile name. Click it.

Select "Public" to enable anybody, both inside and outside of Facebook, to share the post.

Click "Post" to display the message on your wall after finishing.