The period of Spanish, known as el punto, is used similarly to the period of English, although there are differences. Its main uses are to indicate the end of sentences and abbreviations.
In more detail, the period is used:
To indicate the termination of sentences that aren't questions or exclamations.
- El presidente amenaza a los blogueros. The president is threatening the bloggers.
- El español ha dado su primera rueda de prensa. The Spaniard has given his first press conference.
- Descubre los grandes secretos del arte. Discover art's great secrets.
- Me gritó: "El mundo va a terminarse". He shouted to me, "The world is going to end."
- No he leído "El origen de las especies". I have not read "On the Origin of Species."
- Los protones tienen un espín. (Los electrones también tienen un espín). Esta propiedad se aprovecha en la espectroscopía de resonancia magnética nuclear. Protons have spin. (Electrons also have spin.) This property is used to an advantage in magnetic resonance imaging.
To indicate the end of an abbreviation. Periods are not required for abbreviations that are made up of capitalized initials, although some writers use them. If a sentence ends in an abbreviation, only one period is used, not two. (In the sample sentences, abbreviations used are Ud. for usted, etc. for etcétera and ONU for Organización de las Naciones Unidas.)
- Si Ud. quiere aprender inglés, la escuela le ofrece esta oportunidad. If you want to learn English, the school offers you this opportunity.
- Tengo preguntas sobre conjugaciones verbales, adverbios, preposiciones, etc. I have questions about verb conjugations, adverbs, prepositions, etc.
- La subsecretaria general de la ONU confirmó hoy la muerte de catorce de los trabajadores. The subsecretary-general of the U.N. today confirmed the death of 14 of the workers.
In time and calendar references. Although practices vary with region and from publication to publication, it is common to use periods to separate hours from minutes. Thus the time 9:45 is often written as 9.45. The period can also be used in writing dates when all numbers (months not spelled out) are used. Thus Dec. 7, 1941 (possibly written as "12/7/1941" in the U.S.), might be written as 7.12.1941 by a Spanish-speaking writer. Hyphens or slashes are sometimes used instead, as they are in English.
Primary reference source: Diccionario panhispánico de dudas published by the Real Academia Española.