When you sign up for Twitter, your Tweets are public by default; anyone can view and interact with your Tweets. Should you choose to protect your Tweets, you can do so through your account settings.
If you protect your Tweets, you’ll receive a request when new people want to follow you, which you can approve or deny. Accounts that began following you before you protected your Tweets will still be able to view and interact with your protected Tweets unless you block them. Learn more about blocking.
Who can see my Tweets?
Public Tweets (the default setting): Are visible to anyone, whether or not they have a Twitter account.
Protected Tweets: May only be visible to your Twitter followers.
Thanks for the info