Saya mematikan telepon sebelum tidur.

mematikan means to turn off or to switch off. It’s built from:

• Root mati (to die/go off)
• Prefix me-, which turns a root into an active verb
• Suffix -kan, which makes the verb transitive (it needs an object)

So literally mematikan telepon is “cause the phone to go off,” i.e. turn it off.

Indonesian verbs don’t change form for tense. Instead:

• Context or time words (like sebelum tidur) imply when the action happened.
• You can add adverbs if needed:
  
  • kemarin (yesterday)
  • nanti malam (tonight)

Without extra markers, it can be habitual (“I turn off…”) or a single past event (“I turned off…”), depending on context.

Yes. Indonesian word order is flexible for time/place phrases:

• Sebelum tidur, saya mematikan telepon.
• Saya mematikan telepon sebelum tidur.

Both mean I turn off my phone before sleeping. Placing it first simply highlights the time.

Here telepon is clearly the object (“the phone” being turned off). If you want to stress possession, add saya after it:

• Saya mematikan telepon saya sebelum tidur.

But native speakers often drop the possessive when it’s obvious whose phone it is.

Yes, but with nuance:

• telepon: general term for a phone or telephone
• ponsel (from telepon seluler): specifically a mobile/cell phone

Use whichever matches the device you mean.

No. To hang up or end a call, you’d say:

• menutup telepon
• memutuskan panggilan

Mematikan telepon always implies powering off the device, not just ending a call.

• Saya is neutral/formal.
• Aku is informal and intimate.

Both are first-person pronouns, so you can say:

• Aku mematikan telepon sebelum tidur (with friends/family)
• Saya mematikan telepon sebelum tidur (formal or polite contexts)