Probably needs a reset. Just hold in both buttons (front and top) until the phone brings up the Apple symbol then let them go so the phone can reset.
Before you reset you should close all open applications....
This phone has multi-tasking...it opens multiple windows just like a web browser except it does it with the apps.....so every time you use an app it stays open eating into the phones operating memory and slowing it down.....you need to keep and eye on this too by double clicking the home button to bring up the multitasking window and closing down apps you are not using. To do this simply press and hold one until they all wobble, then hit the - symbol to close them. Any you don't want closed that are wobbling leave alone and then hit the home button to steady them and close down this extra screen. You can close them all without doing any harm if you wish as they will open again when you use them. Also the phone will still receive calls and texts as normal.
I should add that the purpose of this window is to allow you to quickly switch to another app when using one...i.e. to send a text message while talking hands free, or to open your contacts to give someone a phone number while chatting...use the camera while using google maps etc..
