Mark Zuckerberg, chief executive officer and founder of Facebook Inc., arrives for a House Financial Services Committee hearing in Washington, D.C., U.S., on Wednesday, Oct. 23, 2019. Andrew Harrer | Bloomberg | Getty Images

Facebook not only uses information from your activity on Facebook and its related products like Instagram to target you with ads, but the company also relies on data from third-party websites to do this. Now, Facebook has rolled out a tool that lets users see exactly which third-party apps and websites share their data with Facebook. The tool also includes a toggle to turn this off. To access the new feature: Tap the down-facing arrow at the top right corner of Facebook.com and click on settings. If you're on mobile, tap the three-line icon at the bottom-right corner of the Facebook app, scroll down and tap "Settings & Privacy" and tap on "Settings."

Click the "Your Facebook Information" heading. On desktop, it's in the left column near the top.

Select "Off-Facebook Activity" heading in the middle of the page.

Next, click on "Manage Your Off-Facebook Activity." This will prompt you to enter your Facebook password.

Facebook's new Off-Facebook Activity tool allows users to see which third-party apps and websites share their data with Facebook and turn it off. Salvador Rodriguez / CNBC

Once in, this page will show you which apps and websites are feeding data to Facebook. You can tap on each app for additional information about how it is sharing data with Facebook, what type of data it is sharing, and what Facebook is doing with that data. These pages will also allow you to download the activity details of what is being shared with Facebook.

If you want to be selective about which apps you prevent, simply click an app that you want off, scroll down and select "Turn off future activity." Repeat this for each website that you want to turn off. Salvador Rodriguez/CNBC

From the "Manage Your Off-Facebook Activity" page, you can delete the third-party websites that have shared with Facebook by simply tapping on the large "Clear History" button at the top of the screen. But this will do little to stop the apps from sharing information with Facebook going forward. To prevent future data sharing, you can either turn everything off or you can turn off data sharing app by app. If you want to be selective about which apps you prevent, simply click an app that you want off, scroll down and select "Turn off future activity." Repeat this for each website that you want to turn off. To turn off future data sharing in bulk, click on "Manage Future Activity," which will prompt a pop up where you should click "Manage Future Activity." This will take you to another page where you can switch a toggle for "Future Off-Facebook Activity."

Salvador Rodriguez/CNBC