To access Salesforce via a desktop application or other API-based application, you must replace your current password with a combination of your password and a security token:
1 Log in to Salesforce via the browser to request your security token.
2 Go to Setup -> My Personal Information -> Reset Security Token.
3 Click the Reset Security Token button to trigger an email which will contain your security token.
4 Select and copy the token from the email.
5 In the application, replace your password with combination of the password and the security token. For example, if your password is "MyPassword" and your security token is "XXXXXX", you would enter "MyPasswordXXXXXX" into the password field.
The security token will be sent to your email address (assuming you're the admin).