Learn Hardcore Russian: Мои наушники лежат на столе.

Наушники is a plural-only noun (like English “glasses”), used for a single pair of headphones.
Because the subject is grammatically plural, the verb must be 3rd-person plural: лежат.
If you mean one earpiece, you can say singular наушник (e.g., Правый наушник сломан).

Why is it мои and not мой?

Мои is the plural form of “my,” agreeing with plural наушники.
Paradigm: мой (masc. sg.), моя (fem. sg.), моё (neut. sg.), мои (plural).
Stress: мои́ (mo-EE).

What is the infinitive of лежат, and how do you conjugate it?

Why use лежат and not стоят, висят, or находятся?

лежат: the item is lying flat on a surface (most natural for headphones on a table).
стоят: the item is standing upright (e.g., a bottle).
висят: the item is hanging (e.g., on a hook).
находятся: neutral “are located,” more formal/impersonal; less natural in casual speech here.

Why is it на столе and not на стол?

What case is столе, and how is it formed?

Is на столу ever correct?

На столу is archaic/poetic or dialectal. In standard modern Russian, say на столе.

Can I change the word order, e.g., На столе лежат мои наушники?

Yes. Both orders are correct.
Starting with На столе emphasizes the location. The neutral meaning stays the same.

Can I drop the verb and say На столе мои наушники?

Yes, it’s grammatical and common. It states identification/existence (“On the table are my headphones”) without describing posture.
With лежат, you explicitly convey “lying.”

Can I omit мои?

Yes: Наушники лежат на столе = “Headphones are on the table.”
Without мои, whether they’re “the/my/some” headphones is resolved by context (Russian has no articles).

How do I say “I put the headphones on the table” and “I took the headphones from the table”?

Put onto (motion to): Я положил(а) наушники на стол. (Accusative after на.)
Took from (motion from): Я взял(а) наушники со стола. (Genitive after с(о).)

Do I need a form of “to be” here, like English “are”?

No. Russian normally omits “to be” in the present.
If you use есть (e.g., На столе есть наушники), it stresses existence (“there exist headphones on the table”), not posture.

How do I pronounce the sentence and where is the stress?

Мои́ (ma-EE), нау́шники (na-OOSH-nee-kee), лежа́т (le-ZHAT), на (na), столе́ (sta-LEH).
Full line: ma-EE na-OOSH-nee-kee le-ZHAT na sta-LEH.

If the headphones are on a hook or stand, do I still use лежат?

On a hook: usually висят (they’re hanging).
On a stand: depends on orientation. If they hang from the stand, висят; if they rest flat on a base, лежат.
Стоят is uncommon for headphones unless they’re clearly upright with a base.

How do I say “I’m wearing headphones”?

Я в нау́шниках. (Prepositional plural after в; idiomatic for wearing.)
Я с нау́шниками means “I have headphones with me,” not necessarily on my head.

Does наушники also cover earbuds and headsets?

Yes. Наушники is the general word for headphones/earphones (over-ear, on-ear, earbuds).
A headset with a mic is often гарниту́ра. Earbuds can be called вкла́дыши or внутриканальные нау́шники.

What are the parts of speech and cases in the sentence?