1. Go to www.twitter.com
2. Log in to your account
3. Go to top right hand side on the black bar on top. Go to where it says your username and click on the arrow pointing down. Click on settings.
4. Now you should be on your settings page. Scroll down until you see "Tweet Privacy." Check the box that says "Protect my tweets" and your tweets won't be available to anyone but your followers.
5. Click Save at the bottom of the page.
6. You have successfully protected your tweets.