I am not able to use iMessage and FaceTime on my iPod touch 4g :( please help me

You really need to provide some details if you want help. Otherwise, look at the articles in this Google search.

https://www.google.com/search?q=iOS%20messages%20troubleshooting

You posted in the iPad forum instead of the iPod forum. I'll request that Apple relocate your post.

Using FaceTime http://support.apple.com/kb/ht4319

Troubleshooting FaceTime http://support.apple.com/kb/TS3367

The Complete Guide to FaceTime: Set-up, Use, and Troubleshooting Problems

http://tinyurl.com/32drz3d

Troubleshooting FaceTime and iMessage activation

http://support.apple.com/kb/TS4268

Troubleshooting Messageshttp://support.apple.com/kb/TS2755

 Cheers, Tom 😉