The underlined words above are demonstrative adjectives (adjetivos demostrativos). The same words when appearing by themselves serve as pronouns (pronombres demostrativos).

All of the above demonstrative pronouns take on the gender of the nouns they represent. When the name of an object is unkown and hence it's gender too, esto is used.

Esto is also used to represent the indefinite- that which doesn't have gender like ideas or events.