Learn Hardcore Turkish: Ben iş ilanı arıyorum.

Ben: I (subject pronoun; optional in Turkish)
iş: job/work
ilanı: advertisement/listing + 3rd‑person possessive suffix -ı → “job advertisement” (literally “advertisement of job”)
arıyorum: I am looking/searching (present continuous of aramak “to look for; to call”)

So: Ben iş ilanı arıyorum. = “I am looking for a job posting.”

Why does ilanı end with -ı? Is that the accusative?

Here -ı is not accusative. It’s the 3rd-person possessive on the head noun of an indefinite compound noun:

Pattern: Noun1 + Noun2-ı/‑i/‑u/‑ü → “Noun2 of Noun1” (category)
Examples: okul çantası (school bag), kahve fincanı (coffee cup), iş ilanı (job advertisement)

Why doesn’t the object have the accusative? When would I say iş ilanını?

In Turkish, a direct object is:

Unmarked when it’s non‑specific: İş ilanı arıyorum. (“I’m looking for job ads (in general).”)
Marked with accusative when it’s specific/definite: İş ilanını arıyorum. (“I’m looking for the job ad.”)

If I add accusative to this compound, why do I get an extra n: iş ilanını?

Because a possessed noun (here ilanı) takes a buffer -n- before case endings:

ilan
- 3sg poss -ı → ilanı
- accusative -ı → ilanını (buffer n)
Full phrase: iş ilanını (arıyorum).

Do I have to say Ben? When would I include or drop it?

You can drop it: İş ilanı arıyorum. Person/number is already on the verb. Use Ben for emphasis or contrast: Ben iş ilanı arıyorum (as opposed to someone else).

Can I change the word order?

Default is Subject–Object–Verb: (Ben) iş ilanı arıyorum.

Moving parts changes focus: İş ilanını ben arıyorum (It’s me who’s looking for the job ad).
Placing the object after the verb (Arıyorum iş ilanı) is unusual in neutral statements and sounds marked or poetic.

Could arıyorum mean “I’m calling” here?

Aramak also means “to call (by phone): Ahmet’i arıyorum = “I’m calling Ahmet.”
In your sentence, iş ilanı arıyorum naturally means “I’m looking for job ads,” not “I’m calling a job ad.” To talk about calling a number from an ad, you’d say: İlandaki numarayı arıyorum (“I’m calling the number in the ad.”)

Why isn’t it plural (ilanları)? I’m probably looking for multiple ads.

In indefinite compounds, the head noun stays singular: iş ilanı already means “job ads” in a general sense.
Use plural only when you’re referring to a specific set: iş ilanlarını arıyorum (“I’m looking for the job ads [we discussed/that I saved]”).

Can I add bir: Bir iş ilanı arıyorum?

You can, but it stresses “a single/one job ad,” which isn’t usually what you mean. The natural way is without bir: İş ilanı arıyorum.

How is arıyorum formed? Why not “arayorum” or “ariyorum”?

Verb: ara- (look for)
Progressive: -(I)yor; vowel harmony picks -ıyor after a back vowel
Vowel raising: final a of the stem raises to ı before -yor → arıyor
1sg ending: -um → arıyorum

So: ara- + -ıyor + -um → arıyorum.

How do I make it negative or ask a question?

Negative: İş ilanı aramıyorum. (“I’m not looking for job ads.”)
Yes/no question: İş ilanı arıyor musun? (“Are you looking for job ads?”)
Question particle mi/mı/mu/mü is separate and follows vowel harmony: arıyor musun / muyum / mu?

How do I pronounce the dotless ı and the letter ş?

ı: a close, back, unrounded vowel (like the “e” in English “the” when unstressed), not like English “i.”
ş: “sh” as in “shoe.”
Stress: with -yor, stress falls on the yor syllable: a-rı-YOR-um.

What’s the difference between iş arıyorum and iş ilanı arıyorum?

İş arıyorum: “I’m looking for a job” (seeking employment). Very common.
İş ilanı arıyorum: “I’m looking for job postings” (browsing listings). Focuses on the ads.

How do I say “I’m looking at/browsing job ads,” not actively searching for one specific ad?

Use bakmak with the dative:

İş ilanlarına bakıyorum. (“I’m looking at job ads.”) Also possible: İş ilanlarını inceliyorum (“I’m reviewing job ads”) if you mean “studying them carefully.”

Why can’t I say iş ilan without -ı?

Indefinite compound nouns require the possessive on the head noun. So it must be iş ilanı, not iş ilan.