Cargo offers primarily a Java API. It is meant to be embdedded in your application. You'll need a JDK 1.4+ and the following jars in your classpath:
If you use the Cargo Ant tasks, you'll also need to add those jars to the <taskdef> definition (see the Ant support page).
To use the Cargo plugin for Maven you'll need to install it (see the Maven1 plugin page).