Saya membaca buku asing di perpustakaan.

Indonesian typically follows a Subject–Verb–Object–(Place) pattern. In this example:

• Saya = Subject
• membaca = Verb
• buku asing = Object
• di perpustakaan = Place/Location

In Indonesian, most adjectives follow the noun they modify. So you say buku asing (literally “book foreign”) rather than asing buku.

Indonesian does not have articles like a or the. Context provides definiteness or indefiniteness. If you want to be explicit, you can add a classifier such as sebuah (a):

• Saya membaca sebuah buku asing di perpustakaan.
  But in most cases you simply say buku asing.

• The root form is baca (read).
• To form a formal active verb, you add the me- prefix. Before a root starting with b, me- assimilates to mem-, giving membaca.
• In casual speech, it’s common to drop the prefix and say Saya baca buku asing..., which native speakers understand to mean the same thing, though membaca is preferred in writing.

• di is a preposition meaning in/at, marking location: di perpustakaan = in/at the library.
• ke means to, marking direction: ke perpustakaan = to the library.

• Preposition di appears with a space and is followed by a noun (location): di rumah, di sekolah.
• Prefix di- attaches directly to a verb (passive): dibaca (is/was read), ditulis (is/was written).
  No space = prefix; space = preposition.

• Saya is formal or polite; safe to use in most settings (meetings, writing, with strangers).
• Aku is informal/intimate; used among friends, family, close peers.
  You could say Aku membaca buku asing... in casual conversation.

Insert an aspect marker like sedang or lagi between the subject and verb:

• Saya sedang membaca buku asing di perpustakaan.
• Saya lagi membaca buku asing di perpustakaan.
  Both convey “I am reading a foreign book at the library right now.”