¡Hola!
Thank you for your questions; you guys have raised some great points.
You’re absolutely right, Scott_C. Both the sentences ¿Me puede decir la hora, por favor? And ¿Puede decirme la hora, por favor? mean “Can you tell me the time, please?”
Direct object pronouns refer to the people or things that are receiving the action in a sentence. For example, in the sentence “I want to send the letter,” the letter is the direct object pronoun and can be changed to “it.” Therefore, the sentence Quiero enviar la carta can become Quiero enviarla “I want to send it” or La quiero enviar “I want to send it.”
Attaching the direct object pronoun to the end of a verb can feel more natural to an English speaker as it more closely resembles the word order rules in English. However, in indicative sentences, attaching the direct object pronoun to the end of a verb is only possible when the sentence uses an infinitive verb, for example, decir “to say” or enviar “to send” or a present participle. The direct object pronoun must come before the verb when the sentence does not contain an infinitive verb or a present participle. For example, Siempre compra las verduras, “He always buys the vegetables," will become Siempre las compra, "He always buys them.”
As for the main difference between a direct object pronoun and an indirect object pronoun, the indirect object pronoun refers to the people or thing to or for whom an action is done. For example, in the sentence Quiero comprar un regalo para Teresa, “I want to buy a gift for Teresa,” the subject is “I,” the verb is “want,” the direct object is “a gift," and the indirect object is “Teresa.” Therefore, this sentence will become Le quiero comprar un regalo, “I want to buy her a gift.” As with a direct object pronoun, the indirect object pronoun can be placed before the conjugated verb or after the infinitive. So Quiero comprarle un regalo, “I want to buy her a gift" is also acceptable. However, neither the direct object pronoun nor the indirect object pronoun may come between the conjugated verb and the infinitive.
I hope this clarifies your question. As Scott_C pointed out, there is a more comprehensive explanation in lesson 5.6 “Me” and “He”: Direct Object Pronouns and in lesson 5.7 “To Me” and “For Her”: Indirect Object Pronouns.
¡Hasta luego!
Indy