Learn Hardcore Turkish: Staj başvurusu için aday formunu doldurdum. - I filled in the candidate form for the internship application.

Staj başvurusu için: a purpose phrase with postposition için = “for the internship application.”
aday formunu: direct object, “the applicant/candidate form,” marked definite with accusative -nı/-ni/-nu/-nü → here -nu.
doldurdum: verb “I filled (it) out” (past tense, 1st person singular).

Why is it başvurusu and not just başvuru?

Because it’s a noun–noun compound (belirtisiz ad tamlaması): staj başvurusu = “internship application.” In such compounds, the head noun takes the 3rd-person possessive suffix -(s)I. Since başvuru ends in a vowel, you add -su: başvuru + su → başvurusu.

Could I say staja başvuru instead of staj başvurusu?

Yes. Two common patterns:

staj başvurusu (compound with possessive on the head)
staja başvuru (noun + dative on the first noun) Both mean “application for/to an internship.” In your sentence you could also say: Staja başvuru için aday formunu doldurdum.

What exactly does için do, and how else is it used?

için is a postposition meaning “for, for the purpose of, because of.” It follows what it relates to:

With nouns: staj için “for an internship”
With pronouns (genitive forms): benim için “for me,” onun için “for him/her”
With verbs (purpose): gitmek için “in order to go,” gelmem için “so that I come”

Why is it aday formunu with -nu at the end?

Two suffixes are stacked:

Compound/possessive on the head: aday formu (candidate form)
Accusative (definite object): -I When a 3rd-person possessed noun takes a case ending, Turkish inserts a buffer -n-: formu + (n) + -u → formunu. So aday formunu = “the candidate form” as a specific, definite object.

Does formunu mean “his/her form”?

By itself, formunu could mean “his/her form” (3rd-person possessed + accusative). In aday formunu, the possessor is the preceding noun aday, forming a compound meaning “candidate/applicant form,” not necessarily one specific person’s form.

Do I have to use the accusative here? What changes if I drop it?

With accusative: aday formunu doldurdum = you filled out a specific, known form.
Without accusative: aday formu doldurdum is grammatical but less natural; it tends to mean “I filled out a candidate form” (non-specific). Learners often mark this explicitly: bir aday formu doldurdum.

What’s the difference between aday formu and başvuru formu?

aday formu: “applicant/candidate form” (a form filled out by the applicant)
başvuru formu: “application form” (the form used to apply) In many recruitment contexts, they refer to the same document.

How would I say “the candidate’s form” (one particular candidate)?

Use the genitive–possessive chain: adayın formu (candidate-GEN + form-3SG.POSS). As a definite object: adayın formunu doldurdum = “I filled out the candidate’s form.”

How is doldurdum formed?

Verb stem: doldur- “to fill (something)”
Past tense: -DI → harmonizes to -du here
1st person singular: -m Result: doldur-du-m → doldurdum = “I filled (it).”

Why is it -du (not -dı/-di/-dü) in doldurdum?

Vowel harmony: the past suffix -DI matches the last vowel of the stem. The last vowel in doldur- is back and rounded (u), so you get -du. Also, the initial consonant of the suffix stays voiced d because the preceding sound (r) is voiced; after a voiceless consonant it would devoice to t (e.g., bak-tı).

How would this change in other tenses?

Present continuous: aday formunu dolduruyorum (I am filling out…)
Future: aday formunu dolduracağım (I will fill out…)
Past continuous: aday formunu dolduruyordum (I was filling out…)
Reported past (evidential): aday formunu doldurmuşum (Apparently I filled it out)

Can I move parts of the sentence around?

Yes, Turkish is flexible. Common variants:

Aday formunu staj başvurusu için doldurdum.
Staj başvurusu için doldurdum aday formunu. The verb typically stays at the end; moving parts shifts emphasis.

Any pronunciation tips for tricky letters here?

ş = “sh” (baŞ…)
ç = “ch” (için)
j in staj = “zh” (as in “measure”) Default stress is often final: staJ, başvuruSU, iÇİN, aDAY, formuNU, doldurDUM.

There’s no “the” or “a” in Turkish—how is that shown here?

Definiteness is signaled by case and context:

aday formunu (accusative) → specific “the.”
bir aday formu (no accusative) → “a/an.” Turkish lacks articles; you rely on the accusative, bir, and context.

Does any word change for gender (male/female applicant)?

No. Turkish has no grammatical gender. aday applies to any gender.