1. Spanish uses the indefinite article (un, una) less frequently than English. Do NOT use it:
- for things normally encountered one at a time.
- before occupations, religions, political affiliation or nationality (used only when such words are qualified by an adjective).
- before otro, otra (another).

2. The definite article (el, la, los, las) is used in Spanish more often than in English. Use it with:
- titles in the third person (el profesor Franco),
- any country that is modified by an adjective (la España moderna),
- any nouns intended in a general sense.

The definite article is often omitted before languages, sports, or fields of knowledge when preceded by the prepositions de and en, and after the verbs hablar, estudiar, tener and saber.

3. The article is generally omitted when the idea of an unspecified amount (some, any in English) is implied:
  There is [some] water - Hay agua   ||   I don't have [any] money - No tengo dinero.

4. The neuter article, lo, is used with an adjective to express abstract concepts, very much like the English "the + adjective + thing": Eso es lo interesante (That is the interesting thing).

—   The prepositions a and de contract with the masculine singular article to form the only two written, mandatory contractions in Spanish, al and del: al norte (a + el)   •   del planeta (de + el)