To be considered for participating in an upcoming short-term missions trip, you'll first fill out an Application online. Applications can be found on each trip's webpage.
After you've submitted your online Application, the Trip Leader will then review your info and make the decision to approve/deny your application.
If approved, you'll then be contacted and asked to officially 'register' for your trip. During the registration process, you may be required to pay a down-payment towards your trip expenses.