Simple app restart can help. To do this, tap on the home button two times, and you will get the preview of apps you have been using lately. Tap on the camera app, and simply swipe up to close it. Go to the Home screen, find the app, and run it again.
If you noticed that your camera app is frozen, maybe you have many other apps which are running in the background, and it can cause a problem. Again, tap on the home button two times, and when you see the list of all the apps which are running, swipe up and close them.
By pressing and holding the sleep/wake button, the slider will show up. Drag it, and restart your device. Once it’s on again, check the camera app. Hopefully, it will work just fine.
If you installed some app recently, and if from that moment the issue with the camera app started, maybe the app you have installed is faulty. Delete the app by tapping on the icon, until an X appears. Click on it, and the app will be gone.
When the new version of iOS is out, get it, and install it. It is extremely beneficial for your device because every new version fixes the issues and bugs of all kinds.