Problem with paypal

Hi
Hi can any body tell me how to integrate pyapal.

i did as follows

This is my check out page

1)

kk

2) when i click the submit button my page is travsersing to paypal , then it is asking for userid. after submiting user credentials

i am clicking pay now button. when i clicked paynow button. i am getting the message as payment has been done successfully.

now here i am getting the probelm .after clicking this pay now button my page dose not travesring to my redirect page, where i am updating the database.Even if the payment is success that is not updating in my databse.

please rectify this error

thanks in advance
chaitu