Please explain articles

1. Indefinite Article (a, an) Used before singular nouns that are unspecified: a pencilan orangeUsed before number collectives and some numbers: a dozena gallonUsed before a singular noun followed by a restrictive modifier: a girl who was wearing a yellow hat Used with nouns to form adverbial phrases of quantity, amount, or degree: I felt a bit depressed. 2. Definite Article (the) Used to indicate a noun that is definite or has been previously specified in the context: Please close the door. I like the clothes you gave me. Used to indicate a noun that is unique: Praise the Lord! The Columbia River is near here. Used to designate a natural phenomenon: The nights get shorter in the summer. The wind is blowing so hard. Used to refer to a time period: I was very nave in the past. This song was very popular in the 1980s. Used to indicate all the members of a family: I invited the Bakers for dinner. This medicine was invented by the Smiths.