¡Hola!
This is a great question! Here is a deeper look at the grammar at play here:
- Quiero algo de tomar. “I want something to drink.”
-
Here, we are seeing the structure algo de + [infinitive] (unconjugated verb). The phrase algo de refers to an unspecified thing here, so it is used to mean "something to" in this context. As long as it suits the context, a different infinitive can follow this phrase, so beber “to drink” would also make sense in this sentence, i.e., Quiero algo de beber “I want something to drink.”
- Quiere usted algo para beber? “Do you (formal) want something to drink?”
-
Para is a preposition usually translated into English as meaning “to” or “for.” There are several different uses of the preposition para, which you can check out in lesson 11.6 Por vs. Para. However, in this context, we are seeing para + [infinitive] (unconjugated verb). When para is used with the infinitive, we can think of it as conveying a goal or purpose and meaning “in order to.” So, although it sounds unnatural, we can think of this phrase in the sense of “I want something in order to drink.” It would also be correct to use a different infinitive here, like tomar, i.e., Quiere usted algo para tomar? “Do you (formal) want something to drink?”
So, in short, you can use either the infinitive verb tomar “to drink” / “to take” or beber “to drink” with either of these structures. In regards to which of these verbs to choose, they both mean “to drink” and will be understood as such; however, it may be useful to note that beber only refers to drinking, while tomar is a bit more flexible and can crop up in many contexts.
There are, of course, regional and country-specific preferences for which phrasing and verb choice are more commonly heard. However, in this context, you will be understood no matter which you choose.
¡Saludos!
Indy