1) Signup in linkedin.com, if not a member in LinkedIn.

2) To create application go to link <a target='_blank' href='https://www.linkedin.com/secure/developer?newapp='>https://www.linkedin.com/secure/developer?newapp=</a> 
  
3) Fill with appropriate details and submit the form.

4) Copy the details under the section "OAuth Keys" to media edit page.