Learn Hardcore Turkish: Misafirler gelmeden masa örtüsünü seriyorum. - I am spreading the tablecloth before the guests arrive.

It’s the negative converb: gel- + -me (NEG) + -den (ABL) → gelmeden.
Core meaning: “without V‑ing.” In time clauses it yields “before V happens,” because the main action occurs while the other action has “not yet” happened.
Example: Yemek yemeden çalışamam = “I can’t work without eating.” Here: “I spread the tablecloth before the guests have come.”

Why not say gelmeyecek (“will not come”) to show the future?

Converbs like -meden don’t carry absolute tense; their time is understood relative to the main verb. Misafirler gelmeden... already means “before the guests arrive.”
Gelmeyecek means “will not come,” which would change the meaning to “before the guests don’t come.”

Is there a difference between gelmeden and gelmeden önce?

Both mean “before (doing/coming).”
gelmeden önce is a bit more explicit and slightly more formal/careful. gelmeden alone is very common and natural.
With longer clauses, ...meden önce can improve clarity.

Why is masa örtüsünü in the accusative?

Turkish marks a definite/specific direct object with -(y)ı/-(y)i/-(y)u/-(y)ü.
Masa örtüsünü seriyorum implies a particular, known cloth. If you mean “a tablecloth” (unspecified), drop the accusative: Masa örtüsü seriyorum.

How is masa örtüsünü built morphologically?

masa “table” + örtü “cover/cloth” form an indefinite compound: masa örtü-sü = “tablecloth” (with 3rd‑person possessive on the second noun).
To mark it as a definite object, add the accusative. Because a possessive is already there, insert the buffer -n-:
- örtü-sü-nü = 3rd poss + buffer -n- + ACC
Full breakdown: masa + örtü + -sü + -n + -ü.

What’s the difference between masa örtüsü and masanın örtüsü?

masa örtüsü: an indefinite compound, the general item “tablecloth” (dictionary-like).
masanın örtüsü: a definite genitive compound, “the cloth of the table” (a particular table’s cloth).

Can I change the word order? Do I need a comma?

All are acceptable:
- Misafirler gelmeden, masa örtüsünü seriyorum.
- Masa örtüsünü, misafirler gelmeden seriyorum.
- Masa örtüsünü seriyorum, misafirler gelmeden.
Meaning unchanged; the order shifts focus. A comma after the initial time clause is optional but common for readability.

Should it be seriyorum or sererim?

seriyorum (present continuous) = “I am (now/soon) spreading it.” Good for a current or near-future action.
sererim (aorist) = habitual/generic: “I (always/usually) spread it before the guests arrive.”

How is seriyorum formed, and how do I pronounce it?

Root: ser- “to spread/lay.”
Progressive: -iyor/-ıyor/-uyor/-üyor by vowel harmony. Here: ser- + -iyor + -um → seriyorum.
Stress: with -yor, primary stress falls on the syllable before -yor: se-ri-yo-rum.

Do the subjects of the two parts have to match with -meden?

No. If the -meden clause names its own subject, it can differ: Misafirler gelmeden, ... (their arriving vs. my spreading).
If you omit a subject, it’s understood to be the same as the main clause: Gelmeden masa örtüsünü seriyorum ≈ “Before I come, I spread the tablecloth.”

How would I say “when” or “until” instead of “before”?

“When”: -ince/-ınca → Misafirler gelince masa örtüsünü seriyorum = “I spread it when the guests arrive” (different timing).
“Until”: -ene/-ana kadar or -inceye/-ıncaya kadar → Misafirler gelene kadar bekliyorum = “I wait until the guests arrive.”

Do I need to add a place like masaya, or is the object alone enough?

The object alone suffices: Masa örtüsünü seriyorum already implies “onto the table.”
To be explicit or contrast locations, you can add one:
- Direction: Masaya masa örtüsünü seriyorum.
- Surface: Masanın üzerine masa örtüsünü seriyorum.
In everyday speech, the extra location is omitted unless needed for emphasis/contrast.

Can I replace masa örtüsünü with a pronoun?

Yes: Onu seriyorum = “I’m spreading it.” Position it before the verb: Misafirler gelmeden onu seriyorum. Make sure context makes o/onu clear.

Why plural misafirler? Could I say just misafir?

misafirler = “the guests” (a particular group).
misafir (singular) can be used generically (“a guest/guests in general”), but if you mean an actual arriving group, plural feels more natural. You can also say misafirlerim (“my guests”) to be explicit.