How to display modal in visualforce page?

Hi Saddam,

If you are using a lookup window to find a contact, what about creating a custom lookup window to which you add a “create contact” button. Use the create button to replace the lookup content with new contact fields right in that window, simple as re-rendering the page using render flags. That way its in keeping with standard salesforce UX and your users will possibly embrace the custom functionality more easily.

For more refer:-https://developer.salesforce.com/forums/?id=906F0000000g3AmIAI