The verb fare can be followed by an infinitive to express the idea of having someone do something or having something done.  If the object is a noun, it follows the infinitive; but if the object is a pronoun, it precedes the verb fare.  (Unless the object pronoun is loro, then it always follows the infinitive.)  Note that farsi can also be used in a causative construction when one is having something done to oneself.

Abbiamo fatto fare quelle sedia.  We had that chair made.
Faccio studiare i ragazzi.  I make the boys study.
Li faccio studiare.  I make them study.
Mi faccio tagliare i capelli.  I'm having my hair cut.

When a causative sentence has two objects, the person being made to do something becomes the indirect object.  In Italian, the indirect object is introduced by a.

Il maestro fa leggere lo studente.  The teacher makes the student read.
Il maestro fa leggere la lettura allo studente.  The teacher makes the student read the passage.

To avoid ambiguity with the indirect object, the preposition da instead of a can be used.  The sentence Abbiamo fatto mandare il pacco a Maria can mean two things:  1) We had Mary send the package or 2) We had the package sent to Mary.  If the first meaning is intended, then da can replace a.