DEMONSTRATIVE PRONOUNS
Demonstrative pronouns include 'this', 'that', 'those', and 'these'. ('that car', 'these books', etc.)

esto:  this   (neuter, unknown object)
ste: this one
stos:  these (plural)
sta: this one (feminine)
stas:  these (feminine plural)

eso: that   (neuter, unknown object)
se: that one
sos:  those (plural)
sa: that one (feminine)
sas: those (feminine plural)

aquello: that over there  (neuter, unknown object)
aqul: that one over there
aqullos: those over there (plural)
aqulla: that one over there (feminine)
aqullas: those over there (feminine plural)


In English, we usually just make two distinctions: between this thing (close by) and that thing (in the distance, or close to the person 
 spoken to). In Spanish, three distinctions are usually made: ste (this thing close by), se (that thing close to the person spoken to) and aqul (that thing in the distance). You will recall that the demonstrative adjectives (este libro, esa mesa, etc.) do NOT carry accent marks. The use of accent marks on these pronoun forms is considered optional in some grammar books.

The 'neuter' demonstrative pronoun:
Neuter demonstrative pronouns also exist: esto (this thing), eso (that thing, near the person spoken to), aquello (that thing in the distance). These neuter never carry a written accent mark. They are used to refer to something unknown (as in the first sentence below), or to refer to a general situation, or an abstract concept or something said earlier (as in the last example below). 

Examples: 
Qu es eso?: What's that [in your hand]?
Eso es ridculo.: That [what you just said] is ridiculous.


The demonstrative pronoun ste/a can be used for 'the latter' and se/a or aqul/la for 'the former'. (Note that in English the order is usually the former ... the latter, whereas in Spanish it is usually the other way around: sta... sa...). 
 
