Types of pronoun
Subject Replaces the subject of the sentence yo (I), tú (you), él (he), ella (she), ellas (they), ellos (they).
Object Functions as the object of the verb or preposition me ( me), te (you), lo (him, it, you), la (her,it, you), le (to him/her/it, you),
  It's common to categorise it into direct and indirect nos(us), os(you), los(them), las(them), les(to them/you).
Demostrative Replaces the noun while olso pointing to it éste (this one), ésta (this one), ése/ésa (that one), aquéllos/aquellas (those ones).
Reflexive  When the direct or indirect object of the verb  me ( myself), te (yourself), se ( himself, herself, themselves).
refer to the same parson  
Possessive Refers to something owned or possessed  mío ( mine), míos (mine), mía (mine), mías (mine), suyo (his, hers, theirs).
by someone  
Indefinite Refer to nonspecific people or thing algo (something), nadie (nobody), alguien (somebody), todo (all), todas (all),
 uno ( one),  unos (some), ninguno (none).
Relative Introduce a clause that gives more information que (that, which, who, whom), quien (who, whom), cuyo (whose), cuyas (whose), 
about a noun or pronoun donde (where), lo cual (which, that which).
Interrogative Used in questions Qué (what), quién (who), cuándo (when), 

Many of the pronouns can have more than one translation, and not all are listed in the examples.
Many of the pronouns exist in masculine, feminine and (rarely) neuter forms
The subject pronouns in Spanish are:
you (familiar)  
you usted.Ud. (formal)  
he él    
she ella    
we nosotros (men or men and women)  
you vosotros (men or men and women) (familiar)  
they  ellos (men or men and women)  
they ( fem) ellas    
you ustedes.Uds. (men or men and women) (formal)  
In Spanish, the subject pronouns indicate the gender and number of the subject.
Generaly it refers to a person, animal or object in a sentence
Is used to replace the proper noun.
Subject pronouns are used in the following instances:
To avoid ambiguity:
 If the sentence makes the subject clear, the pronouns normally wouldn't be used, but,
some verbs forms are ambiguos, ( Indicative - preterite imperfect,  Subjuntive - present) 
on first and thirst person singular have the same form.
"caminaba" (to  walk) could mean "yo caminaba", "él caminaba", "ella caminaba".
"comía" ( to eat) could mean "yo comía", él comía", "ella comía"
"corra" ( to run) could mean " que yo corra", " que él corra", " que ella corra"
"brinde" ( to toast), "cuando yo brinde", " cuando él brinde"
Without the pronoun, it is impossible to tell whom is  the doer of the action that the sentence refers to.
For emphasis
A strong emphasis is placed on "yo" in "Yo lo voy a arreglar"  I´m going to fix it.
 "yo" and not somebody else
the understood meaning of the sentence might be "yo"
"Nosotros " pedimos permiso para usar el salón. We ask permission to use the room.
"Tú" pasarás a buscar a los niños. You will pick up the children.
To differentiate subjects
When contrasting two subjects in the sentence, the pronouns are frequently used.
Yo cocino y tú lavas los platos I'm cooking  and you wash the dishes
Nosotros viajamos a las 22 hs, ustedes viajan 2 horas mas tarde. We travel at 10 pm, and you travel 2 hours later.
To add politeness
Sometimes are not strictly necessary, but included "usted" and "ustedes", add a degree of politeness
¿Cómo está usted? How are you?
Ustedes son los primeros invitados You are the first guests.

page 3 of 9