You can find the Javascript snippet when you log in to your Surfly account.

Click on the 'Settings' link on the menu bar to the left of the screen, then select 'Integration.' You may have to click 'Generate API Keys' before the Javascript snippet is shown.

You will also have to add your website's domain name to the 'Specify Domain Names' section just below the code snippet.

When that's done, click 'Update.' You should see the snippet now.