SUBJECT PRONOUNS:
Subject pronouns are used as the subject of a verb (the verb may be implied). Subject pronouns are also used as the predicate complement after the verb 'ser'. 

yo: I
t: you (familiar, singular)
l: he
ella: she
ellos: they (males, or males and females)
ellas: they (all females)
usted: you (formal, singular)
ustedes: you all (formal, plural)
nosotros, nosotras:  we
vosotros, vosotras: you all (familiar, plural, Spain)

Note the accent marks over t and l.  The 'vosotros' form is used as the plural of 't' in Spain. In Latin America, 'ustedes' is used as the plural of both 'usted' and ''t'. 

Examples: 
Yo prefiero coca-cola.:  I prefer Coca-cola.
Es ella?:  Is it her? [Is it she?]
Quin lo hizo? Yo.:  Who did it?  I did.


In English the subject pronoun 'it' is used very frequently. In Spanish, if the pronoun 'it' does not refer back to anything at all, then 'it' is NOT expressed at all.

Example:
Es obvio que est nevando.:  It's obvious that it is raining. ['It' refers to nothing and is not expressed in Spanish.]


