This document discusses direct and indirect objects in sentences. It explains that:
1) Direct objects are nouns affected by the action of the verb, usually things, while indirect objects are nouns receiving the benefit of the action, usually people.
2) Some verbs like "give" and "buy" can take both a direct and indirect object, in either order.
3) Other verbs like "explain" are followed by the object and then "to", not an indirect object.
4) The preposition "for" can indicate either benefit or acting on behalf of someone.