On a web browser:
Log in to your Twitter account on
https://twitter.com/?lang=en.
Click on "More" (three dots) located on the left side menu.
Select "Settings and privacy" from the pop-up menu.
Choose "Privacy and safety" from the options.
Under "Audience and tagging," check the box next to "Protect your Tweets."
Click on "Protect" to confirm the change.
On the mobile app (iOS and Android):
Open the Twitter app and tap on your profile picture in the top left corner.
Select "Settings and privacy" from the menu.
Choose "Privacy and safety" from the list of options.
Toggle the switch next to "Protect your tweets" to activate it.
Enter your password when prompted and tap "Save changes" to confirm.
Once you make your account private, only your approved followers will be able to see your tweets and your profile information. You'll also need to approve any new follower requests before they can see your content.