In general, the definite article (el, la, los, las) is used in Spanish the same way it is in English. In the following cases, however, it is used in Spanish but not in English (Realidades III p 387)
1. When people are referred to by name and an accompanying title, preceding the title (but not when people are addressed directly using a title):
La profesora Estévez enseña ciencias.
Buenas tardes, doctor Zabala
2. Before the name of a street, avenue, park, or other proper names:
Los vecinos de la calle Ramos se quejaron
3. Before any noun representing an entire species, institution, or general concept:
El perro es el mejor amigo del hombre
La educación es muy importante
4. With certain time expressions:
LLego a las siete de la tarde (hours)
Van a reunirse el lunes próximo (days)
Me encanta la primavera (seasons)
Salió de su país a los diez años (age)
5. When it is an inseparable part of the name of a country, such as El Salvador and of some cities, such as El Cairo, La Habana, El Havre, La Haya, La Paz.
6. The words al and del result from contracting the prepositions a and de with the article el, but there is no contraction when El is part of a proper name.
Vamos al parque
Venimos del bosque
Vamos a El Paso
Venimos de El Paso
7. With the name of languages when used as the subject of a sentence but, not after certain verbs (hablar, estudiar, aprender, entender, enseñar) unless modified by an adverb (Situaciones p 19.)
El español es un idioma importante
Adela habla inglés
Adela habla bien el inglés
8. With reflexive verbs or verbs that use indirect object pronouns (gustar, interesar, encantar)
Me lavo las manos
Ramón se quita la chaqueta