First, before you download or use any app, look at what information it wants. Does it really need your friend list? Your birthday? Your employer? Access to post on your Facebook account?
If it's too late for that and you already have the app on Facebook:
Go to your Facebook page on a desktop computer
Look in the upper right hand corner and click on the little upside down arrow. That will open a menu.
Go to settings and click on it
On the settings page, look at the menu on the left side of the screen and click on apps
How many apps do you see? Do you remember downloading all of these?
You can edit the settings or remove each app
If you're on Facebook mobile:
Open your Facebook app
Click on the "more" menu in the lower right corner
Scroll down to settings, click on it and another menu pops up, click on account settings
Scroll down to apps, click on it
At the top of the page, you should see "Logged in with Facebook," open that
Now you'll see what apps have access to your Facebook info
Click on any app you want to remove, in this case, the one that says vonvon
Scroll down to the bottom and click on "remove app"