A CriteriaQuery is executed in a similar fashion to a string-based JPQL query via the EntityManager and Query interfaces.
EntityManager em = ... Query query = em.createQuery(qdef); List result = query.getResultList();
A query definition can use named parameters, and the parameter values are set as usual in the Query instance.
A developerworks article explains details and further usage of Criteria API and its OpenJPA extensions.