Why I can't open my Facebook & Instagram apps in my IPhone 4S ??

Returning to the home screen after trying to open an app indicates the app has crashed.

Check Settings > General > Usage and make sure you have a reasonable amount of space on your iPhone.

Also, see these tips:

http://readwrite.com/2013/10/15/ios-7-fixes-iphone-4-4s

To manage photos, you can start with Settings > General > Usage > Photos & Camera. That should itemize a bit better where the photos are that take the space. Camera Roll is local to your iPhone, so if you delete photos from there, expect them to be deleted everywhere. Other accounts may be saved other places in addition to your iPhone, and may be safer to delete. It just depends on your personal setup - what accounts you use and where they are stored in addition to your iPhone.

Another thought is possibly these other accounts can stay where they are on other devices (your PC, for example), and simply stop syncing them to your iPhone. You can set all that up pretty simply in iTunes on your computer when your iPhone is connected -- simply choose the Photos tab in the iPhone's area and change the sync rule.

This happened to me as well. Both FB messenger and Care.com apps would begin to open but then shrink before fully opening. The problem: i needed to install updates. Try this if you haven't. (I tend to ignore updates for awhile). Anyhow- once I actually did it, my apps were opening just fine.

Basics from the manual are restart, reset, restore.

You should be importing all pics to your computer regularly as you would with any digital camera. You should be storing everything on your computer.