In Spanish, same as in English, we have two kinds of articles, definite and indefinite. The difference between the 2 can be seen in these two sentences:

The first sentence indicates that if there is a plate of biscuits in front of you, you just want one regardless of the many varieties available. The second sentence indicates that if there is a plate of biscuits in front of you, you only want the chocolate one. So, basically, the difference between definite and indefinite articles is that of specific versus general.

In Spanish, there are 4 different forms for the definite and indefinite articles:

DEFINITE – DETERMINADOS

INDEFINITE – INDETERMINADOS

The 4 forms of the definite article are the equivalent of the English "THE" and the 4 forms of the indefinite article are the equivalent of the English "A" (singular) and "SOME" (plural). "UN" and "UNA" can mean either "ONE" or "A".

PLEASE NOTE: The masculine plural form of both definite and indefinite articles is used for males or mixed sex groups. Thus, if I say "los niños", I could refer to a group of boys or a mixed group of boys and girls. This does not apply to the feminine form which only denotes females.

PLEASE NOTE: The masculine singular form "EL" contracts with the prepositions "DE" and "A" as follows A + EL = AL and DE + EL = DEL.