Articles may sound confusing, but they are easy to understand. Most people don't know that articles are perhaps the most common words in the English language: "A" and "The" and "Some".
A - un, una
The - el, la
Some (plural of "A") - unos, unas
The - los, las
Like adjectives, articles must agree in number and gender with the nouns they modify, for example:
Un libro - A book (notice that "Un" is singular and masculine to match "Libro" which is also singular and masculine.
Una mesa - A desk ("Una" is singular feminine because it modifies a singular feminine noun, "Mesa")
Unos libros - Some books ("Unos" is plural and masculine, so is "libros")
Unas mesas - Some desks (Same thing here, "Unas" is plural and feminine to match "mesas", the noun it modifies)
This is where we chat about all things Spanish. Feel free to ask a question, challenge me, passionately disagree, or rant about whatever. Just make it interesting.