Cargo offers primarily a Java API. It is meant to be embdedded in your application. You'll need Java SE version 5 or greater.
In your classpath, Ant 1.5.4 or greater is required.
In the case you're running on Java 5, you will also need Xerces 2.4.0 or greater.
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 Maven2 (commonly referred to as Maven) you'll need to install it (see the Maven2 plugin page).
To use the Cargo plugin for Maven1 (the old Maven) you'll need to install it (see the Maven1 plugin page).