Welcome to all those new here.
The post settings are like Fb so if you don't want the world to see what you're posting, make sure to set them to "friends only" and your future posts will be set to private.
Reminder: the news feed has a drop down arrow. You can choose to see ALL public posts, or only the posts by people/groups/pages you 'follow.' Conversely, to keep your posts OUT of the public posts, set your profile comments to 'friends only' and post in private groups. (Pages can choose whether or not their posts are visible to everyone or just page folowers.)