Learn Hardcore Turkish: Masada ekmek kırıntıları kaldı; kâğıt havluyla hemen sildim. - There were bread crumbs left on the table; I wiped them immediately with a paper towel.

-da/-de is the locative suffix meaning in/on/at.
Vowel harmony chooses -da after back vowels (a, ı, o, u) and -de after front vowels (e, i, ö, ü).
If the noun ends in a voiceless consonant (p, ç, t, k, f, s, h, ş), the suffix devoices to -ta/-te (consonant harmony): parkta, şehirde, masada.

Why is it ekmek kırıntıları and not ekmek kırıntısı? And does kırıntıları mean their crumbs?

ekmek kırıntıları = bread crumbs (plural).
ekmek kırıntısı (singular) often has a partitive feel: some breadcrumb(s), some crumb residue.
Morphology: ekmek (bread) + kırıntı (crumb) + -lar (plural) + -ı (linking possessive required by the compound). Here, -ı does not mean his/her; it’s the standard linker in an indefinite noun–noun compound. So ekmek kırıntıları is not their crumbs.

Who is the subject in Masada ekmek kırıntıları kaldı?

The subject is ekmek kırıntıları. The verb kalmak (to remain) is intransitive; masada is a locative phrase (on the table). Turkish doesn’t need a dummy subject like English there.

Why is the verb kaldı singular when ekmek kırıntıları is plural? Should it be kaldılar?

Turkish usually keeps the verb in third-person singular with inanimate or non-specific plural subjects. Kaldılar is possible but sounds marked and often implies animacy or emphasis; here, kaldı is the natural choice.

What’s the nuance difference between kaldı and vardı?

vardı = there was/there were (simple existence).
kaldı = remained/was left (implies something happened and as a result crumbs were left). So kaldı carries a resultative, leftover nuance that vardı lacks.

Could I use kalmış instead of kaldı? What changes?

kaldı (simple past) = you know/declare it as a fact.
kalmış (evidential past) = you learned it indirectly, discovered it later, or present it with mild surprise. E.g., You arrive and notice crumbs: Masada ekmek kırıntıları kalmış.

Why is there no explicit object after sildim? How would I say it if I want to be explicit?

Objects can be omitted when obvious from context. You could specify:

Wiping the table: Masayı sildim.
Wiping the crumbs: Onları sildim or Ekmek kırıntılarını sildim.
Note the accusative on a possessed compound: kırıntı-lar-ı-nı (plural + compound linker + accusative).

What exactly does kâğıt havluyla mean morphologically? Is ile a separate word or a suffix?

kâğıt havlu (paper towel) + -yla/-yle (with) = kâğıt havluyla (with a paper towel).
ile can be written separately (kâğıt havlu ile) or fused as a suffix (-la/-le after consonants; -yla/-yle after vowels). Here, havlu ends with a vowel, so you get havlu + yla.

Is kâğıt havlu a fixed compound? Why not kâğıt havlusu?

Product names often use a bare noun–noun pattern: kâğıt havlu, kâğıt peçete. The -sı/su linker appears in classic indefinite compounds (e.g., okul kapısı). Kâğıt havlusu would sound like the towel belonging to paper; it’s not how the product name is formed.

Can I change the word order, e.g., Ekmek kırıntıları masada kaldı; Hemen kâğıt havluyla sildim?

Yes. Word order is flexible for emphasis. Starting with Masada foregrounds the location; starting with Ekmek kırıntıları foregrounds the crumbs. The meaning stays the same, with subtle shifts in focus.

Where should hemen go? Does its position affect meaning?

Hemen (immediately) is flexible:

Hemen kâğıt havluyla sildim emphasizes promptness.
Kâğıt havluyla hemen sildim foregrounds the instrument first.
Sildim hemen is colloquial, adding immediacy as an afterthought. The core meaning doesn’t change; word order adjusts emphasis.

Is the semicolon necessary here?

No. You could use a period (…kaldı. …sildim.) or a comma (…kaldı, …sildim) or add ve (and). The semicolon neatly links two closely related independent clauses.

Does Masada mean on the table or at the table? How do I say on top of the table?

Masada can mean on/at the table depending on context. To be explicit about on top of, use masanın üstünde/üzerinde: Masanın üstünde ekmek kırıntıları kaldı.

How do you pronounce kâğıt, and what’s the purpose of the circumflex?

Spelling varies: kâğıt or kağıt. The circumflex can indicate a longer â and palatal quality in some words. In practice, ğ lengthens the preceding vowel; kâğıt sounds roughly like “kaa-ıt,” with the ğ not pronounced as a hard consonant.

Do I need to say ben before sildim?

No. The ending -dim already marks first-person singular. Use ben only for emphasis or contrast: Ben sildim (I wiped it, not someone else).