The Spanish expression "casas para alguilar" translates into English as "houses for rent." The Spanish verb "alquilar" should not be confused with the Spanish noun "alquiler," which is the actual rent paid.
The Spanish word "casas" is the plural form of the singular noun "casa," which means "house." "Para" is a preposition that means "for/to" and is used to connect the noun and the verb of the expression. "Alquilar" is the infinitive form of the verb, which translates into English as "rent." Due to the verb being in its infinite form, it acts as an overarching command, not conjugated for one particular subject.