Tolong simpan uang pas di saku celana.

Tolong is a politeness marker often used to soften requests/commands, very similar to please.

• Tolong + verb = “Please (do) …” / “Could you (do) …”
  It can sound slightly more like “helpfully do this” than English “please,” but in everyday Indonesian it’s a normal polite request.

Because this is an imperative/request. Indonesian commonly uses the bare verb (base form) for commands and requests:

• Simpan uangnya. = “Store/put away the money.”
• Tolong simpan uang… = “Please put away the money…”
  Menyimpan is more common in statements/descriptions:
• Saya menyimpan uang di saku. = “I keep money in my pocket.”

Both can work, but the nuance differs:

• simpan = “store/keep/put away (safely),” often implies keeping it for a while or putting it somewhere more secure/appropriate.
• taruh = “put/place,” more neutral and often more temporary.
  In this sentence, simpan suggests “keep it in your pocket (properly/safely).”

It’s a different use. Here pas is like “right (there) / straight (into) / directly.”
So pas di saku celana means “right in the pants pocket.”
Indonesian often uses pas to emphasize precise placement or timing:

• Pas sampai, hujan. = “Right when (we) arrived, it rained.”
• Pas di sini. = “Right here.”

Both can be possible depending on emphasis:

• di focuses on location/state: “in/at the pocket” (where it should be).
• ke focuses on motion/destination: “into the pocket.”
  In everyday Indonesian, people often use di even when the action implies movement, so simpan … di saku is very natural. If you want to stress “put it into,” ke saku celana is also fine.

Di is the most common preposition for locations, including “in” when the place is understood as a container (like a pocket).
Dalam means “inside” and is more explicit. It’s grammatical, but can sound a bit more “descriptive”:

• di saku celana = natural everyday “in the pants pocket”
• dalam saku celana = “inside the pants pocket” (more explicit)

Both can mean “pocket,” but:

• saku is very common for clothing pockets and sounds neutral.
• kantong is also used for pockets, but it strongly also means “bag/sack” (e.g. plastic bag), so context matters.
  Saku celana is a very standard phrase for “pants pocket.”

Not necessarily. Indonesian often leaves possession implied when it’s obvious from context:

• di saku celana = “in (the/your) pants pocket”
  If you want to specify:
• di saku celanamu = in your pants pocket
• di saku celana saya = in my pants pocket

With tolong, it’s a polite request, but still fairly direct (like “Please put the exact change in your pants pocket.”).
To make it softer, you can add particles or phrasing like:

• Tolong simpan uang pasnya dulu, ya, di saku celana.
• Bisa tolong simpan uang pas di saku celana? (“Could you please…?”)