If you are in the dashboard, go to the tab called "Applications" and look for the application under available applications. If you have already integrated the application, you will be able to see it under "My Applications".
If you are in the Marketplace you can find the application under various categories. You can also search for this application in the search bar.
Once you find the application either in the dashboard or on the Marketplace click on view. You will be taken to a page where you'll find the integrate option/button. Click on the integrate button.
You will be on the integration page which prompts you to add an account to the application. Click add account which takes you to the application OAuth page or you may have to do it using API keys for application that don't have or allow OAuth.
Allow the needed permissions and the application is now integrated with YellowAnt.