When is a personal a required ?
a: the direct object is a thing b: The direct object is a person c: The indirect object is a thing d: The indirect object is a person
1 Answer
In Spanish, when the direct object is a person, it is preceded by the preposition "a." This word has no English translation.
Jorge llama a María. Jorge calls María.
This link has more info on when it is and when it isn't needed, hope it helps 
From the perspective of the English speaker, the personal "a" appears to be an extra word. From the perspective of the Spanish speaker, the personal "a" is required, and to not use it is a serious error.
Jorge llama a María.
The personal "a" may also be used if the direct object is a domesticated animal, especially a pet, provided that the speaker attaches some sort of personal feelings towards the animal.
La mujer acaricia a su perro. (acariciar) The woman pets her dog.
El perro persigue a la gata. (perseguir) The dog chases the cat.
