I can FaceTime from my ipad2 to my iphone4s but I can't FaceTime from my iphone4s to my ipad2 !!!!!! Can you help me please

I'm not certain of this, but I believe that if you are associating the same E mail address with both devices, this will cause the problem you describe.

Review the Settings/FaceTime on each device. Each device should be set to it's own "reached at" and Caller ID. For example your iPhone can use it's phone number then set the iPad to use your Apple ID email address or one of the iCloud addresses. The call will not go through if both devices are set to receive a call on the same address.