Learn Hardcore Vietnamese: Sáng tôi đọc sách ở thư viện. - In the morning, I read books in the library.

sáng means “morning.” Vietnamese typically puts time expressions first to show when the action happens, so starting with sáng tells the listener that the activity takes place in the morning.

Why isn’t there a preposition like vào before sáng?

Although you can say vào buổi sáng, it’s more natural and concise to drop vào (and even buổi) and just use sáng at the start. Native speakers often omit prepositions when the meaning remains clear.

Does sáng here mean “this morning” or “every morning”?

As written, sáng is ambiguous: it can refer to a habitual morning routine or, with context, to “this morning.” To specify “this morning,” you would normally say sáng nay.

How do I make it clear that it was this particular morning?

Add nay after sáng:
Sáng nay tôi đọc sách ở thư viện.
This unambiguously means “This morning I read books at the library.”

What is the role of ở in ở thư viện? Can I use tại or trong instead?

ở is a preposition meaning “at” or “in,” marking location. You could also use tại for a slightly more formal tone: tôi đọc sách tại thư viện. trong emphasizes “inside,” so trong thư viện works if you want to highlight that you were inside the building.

Why is there no tense marker like past or present on the verb đọc?

Vietnamese verbs don’t change form for tense. Instead, you rely on context and time words. Here, sáng (or sáng nay) indicates when the action happened. If you want to stress that it’s already completed, insert the particle đã before the verb:
Sáng tôi đã đọc sách ở thư viện.

What is the basic word order in this sentence?

The pattern is:
Time + Subject + Verb + Object + (Location)
So you get:
Sáng (time) | tôi (subject) | đọc (verb) | sách (object) | ở thư viện (location).

Why is there no classifier before sách? When would I need one?

In đọc sách, sách is used generically (“read books” or “book-reading”), so no classifier is needed. To specify a single book, use a numeral plus a classifier:
Sáng tôi đọc một cuốn sách ở thư viện.
Here một cuốn means “one [book].”

Can I omit tôi and just say Sáng đọc sách ở thư viện?

Dropping tôi is possible in very casual speech if the subject is obvious, but it can sound abrupt. Including tôi makes the sentence clearer and more natural in most contexts.

How do I express that I’m reading books at the library right now this morning?

Use the aspect marker đang before the verb for an ongoing action, and specify nay for “this morning”:
Sáng nay tôi đang đọc sách ở thư viện.
This means “This morning I am reading books at the library [right now].”