Rather than learning how to use a by its translation, it is probably best to learn the purposes for which a is used. Look over the list below for some examples of how a is commonly used. This chart doesn't cover all its uses, but it does show the uses you are most likely to come across at the beginning stages of learning Spanish. Where a is translated, the translation is indicated in boldface. (Note: In a few places below you'll see the contraction al, which is short for a + el.)
- to indicate motion — Almost any verb indicating motion, and even nouns, can be followed by a before the destination. — Llegamos a St. Louis. (We arrived at St. Louis.) Se acercó a la casa. (He got near the house.) Cayó al piso. (It fell to the floor.) Esa es la puerta al baño. (That is the door to the bathroom.) Me siento a la mesa. (I am sitting at the table.)
- to connect a verb with a following infinitive — This use of a is especially common following verbs indicating the start of an action. In these cases, a is not translated separately from the infinitive. — Empezó a salir. (She began to leave.) Entró a hablar contigo. (He came in to talk to you.) Él se negó a nadar. (He refused to swim.) He venido a estudiar. (I have come to study.) Comenzó a bailar. (She began to dance.) Voy a cantar. (I am going to sing.)
- to indicate manner or method — Numerous expressions begin with a followed by a noun to indicate how something is done. The phrase starting with a functions as an adverb and is sometimes translated as one. — Vamos a pie. (We are going on foot.) Hay que fijarlo a mano. (It is necessary to fix it by hand.) Estoy a dieta. (I am on a diet.) Escribo a lápiz. (I am writing with a pencil.) Andan a ciegas. (They are walking blindly.) Llegamos a tiempo. ( We are arriving on time.) Lee el libro a escondidas. (He is studying the book covertly.)
- to introduce a direct object that is a person or treated like a person — This usage is known as the "personal a." The preposition in these cases usually is not translated. — Conozco a Pedro. (I know Peter.) Encontré a Fido. (I found Fido.) Veré a María. (I will see Mary.)
- to introduce an indirect object — Le doy una camisa a Jorge. (I am giving a shirt to George.) Le compro una camisa a Jorge. (I am buying a shirt for George.) Le robo una camisa a Jorge. (I am taking a shirt from George.) Le pongo la camisa a Jorge. (I am putting the shirt on George.)
- in various expressions of time — Salimos a las cuatro. (We are leaving at four.) Estamos a lunes. (Today is Monday.)
Keep in mind that not all uses of a are listed here, and that in some cases other prepositions can be used for the same purpose. As you become more familiar with Spanish, you will come to instinctively know which preposition to use in various circumstances.