Learn Hardcore Spanish (Latin America): Cuando marco el ritmo con la mano, la melodía se queda mejor en mi memoria. - When I mark the rhythm with my hand, the melody sticks better in my memory.

Indicative after cuando for habitual, repeated, or present-time facts.
- Cuando marco el ritmo… = Whenever I mark the rhythm… / When I (usually) mark the rhythm…
Subjunctive after cuando for future or uncertain events.
- Cuando marque el ritmo… = When I mark the rhythm (in the future)…

In this sentence, the speaker is talking about a general habit, so marco (present indicative) is correct.

Why does it say la melodía se queda instead of just la melodía queda?

Both verbs exist:

quedar = to remain, be left, end up (non‑reflexive).
quedarse = to stay, to remain somewhere / in some state (reflexive/pronominal).

With things that metaphorically stay in your mind or memory, Spanish very often prefers quedarse:

La melodía se queda en mi memoria.
= The melody stays / sticks in my memory.

Using se queda makes it sound more natural and emphasizes the idea that it ends up staying there, almost like it settles in your memory.

La melodía queda en mi memoria is understandable, but it sounds a bit less idiomatic in this context.

Why is it la mano and not mi mano for with my hand?

With parts of the body and clothing, Spanish usually uses the definite article (el / la / los / las) instead of a possessive:

Me lavo las manos. = I wash my hands.
Cerró los ojos. = He/She closed his/her eyes.

Possession is already clear from the subject (yo, me, etc.), so you don’t need mi.

In your sentence, it’s understood that you are using your own hand:

…con la mano… = with my hand (in English).

You can say con mi mano for extra emphasis or contrast, but con la mano is the neutral, most natural version.

Why do we say la melodía instead of just melodía without an article?

In Spanish, a singular, countable noun almost always needs some determiner:

la melodía (the melody)
una melodía (a melody)
esta melodía (this melody)

Bare nouns (without article) are far less common than in English. English often says:

Melody stays in my memory (no article)

Spanish normally requires the article here:

La melodía se queda mejor en mi memoria.

We assume we’re talking about a specific melody (for example, the one you are listening to or learning), so la is used.

What exactly does marcar el ritmo mean? Could I say hacer el ritmo or llevar el ritmo instead?

Marcar el ritmo is a very common expression meaning:

to mark the beat / keep time / tap out the rhythm.

Typical contexts:

Marcar el ritmo con la mano / con el pie / con un lápiz.

Alternatives:

Llevar el ritmo – to keep the beat; often about staying in time with music.
Seguir el ritmo – to follow the rhythm.

Hacer el ritmo is not idiomatic in this context and would sound odd.
So here:

marcar el ritmo con la mano is the most natural expression for tapping or indicating the beat with your hand.

What does mejor express here? Why not más or más fácilmente?

Mejor is the comparative of bien and bueno and often means:

better / more effectively / more easily, depending on context.

In se queda mejor en mi memoria, mejor can imply:

It stays better in my memory (more firmly, more clearly, more easily).

You could also say:

…se queda más fácilmente en mi memoria. = it stays more easily in my memory.
…se queda más en mi memoria. = it stays more in my memory (slightly different nuance).

But mejor is short and natural and nicely captures the idea of it works better this way.

Is the word order se queda mejor en mi memoria fixed, or could I say se queda en mi memoria mejor?

Spanish word order is flexible, but there are more natural patterns.

The usual place for short adverbs like mejor is right after the verb:

se queda mejor en mi memoria ✅ (most natural)
se queda en mi memoria mejor 😐 understandable but sounds a bit clunky.

You might move mejor for special emphasis, but in neutral speech Verb + mejor + rest of the phrase is best.

Why en mi memoria and not en la memoria or en mi mente?

All three are possible, but with slightly different feels:

en mi memoria – focuses on your capacity to remember, your memory as a personal store.
en la memoria – more general or impersonal; can sound like in the memory in an abstract sense.
en mi mente – in my mind; a bit more psychological or mental-image focused.

Here, en mi memoria matches the idea that the melody is being retained or stored in your personal memory, which is why it’s the most natural choice.

Is the comma after Cuando marco el ritmo con la mano required?

Yes, in standard Spanish punctuation it is normal and recommended:

When a subordinate clause (starting with cuando, si, porque, aunque, etc.) comes before the main clause, you usually separate them with a comma:
- Cuando marco el ritmo con la mano, la melodía…
- Si estudias todos los días, vas a aprender más.

If the main clause comes first, you usually omit the comma:

La melodía se queda mejor en mi memoria cuando marco el ritmo con la mano.

Could we say Cuando marcaba el ritmo con la mano? How would that change the meaning?

Yes, but the nuance changes:

Cuando marco el ritmo con la mano… (present)
– Describes a current, general habit: Whenever I (nowadays) mark the rhythm…
Cuando marcaba el ritmo con la mano… (imperfect)
– Describes a past habit or repeated action: Whenever I used to mark / When I used to mark the rhythm…
– The rest of the sentence would normally also be in a past tense:
- …la melodía se quedaba mejor en mi memoria.

So marco = habit in the present; marcaba = habit in the past.

What does the expression quedarse en la memoria or quedarse en mi memoria generally mean?

Quedarse en la memoria / en mi memoria is a common expression meaning:

to remain in (my) memory,
to stick in (my) memory,
to be memorable.

Examples:

Ese día se quedó para siempre en mi memoria.
Los detalles no se me quedaron en la memoria.

In your sentence, la melodía se queda mejor en mi memoria means the melody sticks better, or is easier to retain, when you mark the rhythm with your hand.