How to setup and trigger the hook manually
Sometimes you need to setup the service hook manually. Normally this should not be necessary as you should be able to started simply flip the relevant switch on the profile page.
However especially when setting up an repository hosted inside a github organization the hook needs to be setup manually. Simply access the given repositories admin panel on github. Then access the "service hooks" section.
The URL will look something like https://github.com/[your organization]/[your repository]/admin/hooks.
As the list is very long you will need to scroll down and after clicking on "Travis" scroll back up. You will be presented with a form with 3 fields: Domain, User, Token.
You can leave the Domain empty. In the User field enter the github account you used to authenticate yourself on travis-ci.org. In the Token field paste the token as it is listed on the profile page on travis-ci.org.
When you click "Update Settings" the hook is setup and from now on pushes to this repository will trigger a build on travis-ci.org.
Clicking on "Test Hook" will trigger a build on your "master" branch without having to push. Note this will also work if you setup your hook via the switches on your profile page.