Saya letak pinggan bersih di atas meja makan.

Malay verbs do not change form for past, present, or future. Context or time words signal the tense. In this sentence, without a time adverb it’s interpreted as a simple statement of fact (often past). To clarify timing you can add:

• sudah (already) → Saya sudah letak… (I have put / I already put)
• akan (will) → Saya akan letak… (I will put)

In Malay the normal order is Noun + Adjective. So:
• pinggan bersih = plate clean = clean plate.
You may insert yang for emphasis or formality:
• pinggan yang bersih = the plate that is clean

di atas is the locative preposition “on.”

• di marks location, roughly equivalent to “on/at.”
• atas means “above” or “on.”
  Standard usage: di atas meja.
  In casual speech people sometimes drop di and say atas meja, but di atas is more correct.

Malay does not use articles (a, an, the). Definiteness or specificity is shown by:
• Context
• Demonstratives: ini (this), itu (that)
Example: pinggan ini = this plate; meja itu = that table

meletakkan is the formal/dictionary form (with the me-...-kan affixes).
In everyday, colloquial Malay speakers often use the bare root verb:
• Informal: Saya letak pinggan…
• Formal/Written: Saya meletakkan pinggan…

Both mean “I put the plate…,” but the second is more formal.

meja makan is a compound noun meaning dining table.
• meja = table
• makan = to eat
Combining them specifies the table’s purpose (eating).

Yes. Insert sudah or telah before the verb:
• Informal: Saya sudah letak pinggan bersih di atas meja makan.
• Formal/Written: Saya telah meletakkan pinggan bersih di atas meja makan.

Yes, but register changes:
• Saya = polite/formal first-person pronoun.
• Aku = informal/intimate pronoun (friends, family, casual).

Use saya when you want to be polite or are not close to the person.